diff --git a/lib/tree.rb b/lib/tree.rb
index c0d4b51..a7a62e8 100644
--- a/lib/tree.rb
+++ b/lib/tree.rb
@@ -16,51 +16,225 @@ def initialize
     @root = nil
   end
 
-  # Time Complexity: 
-  # Space Complexity: 
+  # Time Complexity: O(log n)
+  # Space Complexity: O(n)
   def add(key, value)
-    raise NotImplementedError
+    @root = add_helper(@root, key, value)
   end
 
-  # Time Complexity: 
-  # Space Complexity: 
+  # def add(key, value)
+  #   new_node = TreeNode.new(key, value)
+  #   current = @root
+  #   if current.nil?
+  #     current = new_node
+  #   else
+  #     done = false
+  #     until done
+  #       if key <= current.key
+  #         if !current.left.nil?
+  #           current = current.left
+  #         else
+  #           current.left = new_node
+  #           done = true
+  #         end
+  #       else
+  #         if !current.right.nil?
+  #           current = current.right
+  #         else
+  #           current.right = new_node
+  #           done = true
+  #         end
+  #       end
+  #     end
+  #   end
+  #   return current
+  # end
+
+  # Time Complexity: O(log n)
+  # Space Complexity: O(n)
   def find(key)
-    raise NotImplementedError
+    return find_helper(@root, key)
   end
 
-  # Time Complexity: 
-  # Space Complexity: 
+  # def find(key)
+  #   current_node = @root
+  #   if current_node.nil?
+  #     return nil
+  #   else
+  #     while true
+  #       if current_node.key == key
+  #         return current_node.value
+  #       elsif current_node.key > key
+  #         if current_node.left.nil?
+  #           return false
+  #         else
+  #           current_node = current_node.left
+  #         end
+  #       else
+  #         if current_node.right.nil?
+  #           return false
+  #         else
+  #           current_node = current_node.right
+  #         end
+  #       end
+  #     end
+  #   end
+  # end
+
+  # Time Complexity: O(n)
+  # Space Complexity: O(n)
   def inorder
-    raise NotImplementedError
+    inorder_helper(@root, [])
   end
 
-  # Time Complexity: 
-  # Space Complexity: 
+  # Time Complexity: O(n)
+  # Space Complexity: O(n)
   def preorder
-    raise NotImplementedError
+    preorder_helper(@root, [])
   end
 
-  # Time Complexity: 
-  # Space Complexity: 
+  # Time Complexity: O(n)
+  # Space Complexity: O(n)
   def postorder
-    raise NotImplementedError
+    postorder_helper(@root, [])
   end
 
-  # Time Complexity: 
-  # Space Complexity: 
+  # Time Complexity: O(n)
+  # Space Complexity: O(2n) or O(n)
   def height
-    raise NotImplementedError
+    return height_helper(@root)
   end
 
   # Optional Method
-  # Time Complexity: 
-  # Space Complexity: 
+  # Time Complexity:
+  # Space Complexity:
   def bfs
     raise NotImplementedError
   end
 
+  def delete(key)
+    parent = nil
+    current = @root
+    # find the node, keeping track of its parent
+    result = find_with_parent_helper(current, parent, key)
+    return nil if result.nil?
+    current = result[:current]
+    parent = result[:parent]
+    # if the found node has no children
+    #   - if the node was parent.right, set parent.right to nil
+    #   - if the node was parent.left, set parent.left to nil
+    if current.left.nil? && current.right.nil?
+      (parent.right == current) \
+      ? parent.right = nil \
+      : parent.left = nil
+    # else if the found node has 1 child
+    #   - if child is .right, point parent.right to the child
+    elsif !current.right.nil? && current.left.nil?
+      (parent.right == current) \
+      ? parent.right = current.right \
+      : parent.left = current.right
+    #   - if child is .left, point parent.left to the child
+    elsif !current.left.nil? && current.right.nil?
+      (parent.right == current) \
+        ? parent.right = current.left \
+        : parent.left = current.left
+    else
+      # else if the found node has 2 children
+      #   - find the right child's leftmost leaf
+      right_child = current.right
+      leftmost_left = right_child.left
+      until leftmost_leaf.left.nil?
+        leftmost_leaf = leftmost_leaf.left
+      end
+      #   - copy leftmost leaf to item to delete
+      current.value = leftmost_leaf.value
+      #   - change right child's .left to point to leftmost leaf's .right
+      right_child.left = leftmost_leaf.right
+      #   - garbage collector deletes current
+    end
+  end
+
   # Useful for printing
   def to_s
     return "#{self.inorder}"
   end
+
+  private
+
+  def find_with_parent_helper(current_node, parent_node, key)
+    return nil if current_node.nil?
+    return {"current": current_node, "parent": parent_node} if current_node.key == key
+
+    if key <= current_node.key
+      return find_with_parent_helper(current_node.left, current_node, key)
+    else
+      return find_with_parent_helper(current_node.right, current_node, key)
+    end
+  end
+
+  def add_helper(current_node, key, value)
+    return TreeNode.new(key, value) if current_node.nil?
+
+    if key <= current_node.key
+      current_node.left = add_helper(current_node.left, key, value)
+    else
+      current_node.right = add_helper(current_node.right, key, value)
+    end
+
+    return current_node
+  end
+
+  def find_helper(current_node, key)
+    return nil if current_node.nil?
+    return current_node.value if current_node.key == key
+
+    if key <= current_node.key
+      return find_helper(current_node.left, key)
+    else
+      return find_helper(current_node.right, key)
+    end
+  end
+
+  def inorder_helper(current_node, list)
+    return list if current_node.nil?
+
+    inorder_helper(current_node.left, list)
+    list << { key: current_node.key, value: current_node.value }
+    inorder_helper(current_node.right, list)
+
+    return list
+  end
+
+  def preorder_helper(current_node, list)
+    return list if current_node.nil?
+
+    list << { key: current_node.key, value: current_node.value }
+    preorder_helper(current_node.left, list)
+    preorder_helper(current_node.right, list)
+
+    return list
+  end
+
+  def postorder_helper(current_node, list)
+    return list if current_node.nil?
+
+    postorder_helper(current_node.left, list)
+    postorder_helper(current_node.right, list)
+    list << { key: current_node.key, value: current_node.value }
+
+    return list
+  end
+
+  def height_helper(current_node)
+    return 0 if current_node.nil?
+
+    left_height = height_helper(current_node.left)
+    right_height = height_helper(current_node.right)
+
+    if left_height >= right_height
+      return left_height + 1
+    else
+      return right_height + 1
+    end
+  end
 end
diff --git a/test/tree_test.rb b/test/tree_test.rb
index 345bf66..a33dd53 100644
--- a/test/tree_test.rb
+++ b/test/tree_test.rb
@@ -13,7 +13,7 @@
     tree
   }
 
-  describe "add and find" do 
+  describe "add and find" do
     it "add & find values" do
       tree.add(5, "Peter")
       expect(tree.find(5)).must_equal "Peter"
@@ -28,6 +28,12 @@
     it "can't find anything when the tree is empty" do
       expect(tree.find(50)).must_be_nil
     end
+
+    it "can't find anything when the tree doesn't have the item" do
+      tree.add(5, "Peter")
+      tree.add(15, "Ada")
+      expect(tree.find(50)).must_be_nil
+    end
   end
 
   describe "inorder" do
@@ -36,8 +42,8 @@
     end
 
     it "will return the tree in order" do
-      expect(tree_with_nodes.inorder).must_equal [{:key=>1, :value=>"Mary"}, {:key=>3, :value=>"Paul"}, 
-                                       {:key=>5, :value=>"Peter"}, {:key=>10, :value=>"Karla"}, 
+      expect(tree_with_nodes.inorder).must_equal [{:key=>1, :value=>"Mary"}, {:key=>3, :value=>"Paul"},
+                                       {:key=>5, :value=>"Peter"}, {:key=>10, :value=>"Karla"},
                                        {:key=>15, :value=>"Ada"}, {:key=>25, :value=>"Kari"}]
     end
   end
@@ -49,8 +55,8 @@
     end
 
     it "will return the tree in preorder" do
-      expect(tree_with_nodes.preorder).must_equal [{:key=>5, :value=>"Peter"}, {:key=>3, :value=>"Paul"}, 
-                                        {:key=>1, :value=>"Mary"}, {:key=>10, :value=>"Karla"}, 
+      expect(tree_with_nodes.preorder).must_equal [{:key=>5, :value=>"Peter"}, {:key=>3, :value=>"Paul"},
+                                        {:key=>1, :value=>"Mary"}, {:key=>10, :value=>"Karla"},
                                         {:key=>15, :value=>"Ada"}, {:key=>25, :value=>"Kari"}]
     end
   end
@@ -61,26 +67,26 @@
     end
 
     it "will return the tree in postorder" do
-      expect(tree_with_nodes.postorder).must_equal [{:key=>1, :value=>"Mary"}, {:key=>3, :value=>"Paul"}, 
-                                         {:key=>25, :value=>"Kari"}, {:key=>15, :value=>"Ada"}, 
+      expect(tree_with_nodes.postorder).must_equal [{:key=>1, :value=>"Mary"}, {:key=>3, :value=>"Paul"},
+                                         {:key=>25, :value=>"Kari"}, {:key=>15, :value=>"Ada"},
                                          {:key=>10, :value=>"Karla"}, {:key=>5, :value=>"Peter"}]
     end
   end
 
-  describe "breadth first search" do
+  xdescribe "breadth first search" do
     it "will give an empty array for an empty tree" do
       expect(tree.bfs).must_equal []
     end
 
     it "will return an array of a level-by-level output of the tree" do
-      expect(tree_with_nodes.bfs).must_equal [{:key=>5, :value=>"Peter"}, {:key=>3, :value=>"Paul"}, 
-                                   {:key=>10, :value=>"Karla"}, {:key=>1, :value=>"Mary"}, 
+      expect(tree_with_nodes.bfs).must_equal [{:key=>5, :value=>"Peter"}, {:key=>3, :value=>"Paul"},
+                                   {:key=>10, :value=>"Karla"}, {:key=>1, :value=>"Mary"},
                                    {:key=>15, :value=>"Ada"}, {:key=>25, :value=>"Kari"}]
     end
   end
-  
-  describe "height" do 
-    it "will return 0 if tree is empty" do 
+
+  describe "height" do
+    it "will return 0 if tree is empty" do
       expect(tree.height()).must_equal 0
     end
 
@@ -91,7 +97,7 @@
       tree_with_nodes.add(65, "sam")
       expect(tree_with_nodes.height).must_equal 6
     end
-    
+
     it "will give the correct height of a binary search tree" do
       tree_with_nodes.add(30, "Tatiana")
       expect(tree_with_nodes.height).must_equal 5