diff --git a/lib/tree.rb b/lib/tree.rb
index c0d4b51..fe4d89a 100644
--- a/lib/tree.rb
+++ b/lib/tree.rb
@@ -16,47 +16,152 @@ def initialize
     @root = nil
   end
 
-  # Time Complexity: 
-  # Space Complexity: 
-  def add(key, value)
-    raise NotImplementedError
+  # Time Complexity: O(log n) if balanced; O(n) if not
+  # Space Complexity: O(log n) if balanced; O(n) if not
+  def add(key, value = nil)
+    if @root.nil?
+      @root = TreeNode.new(key, value)
+      return
+    end
+
+    add_helper(@root, key, value)
+  end
+
+  def add_helper(node, key, value)
+    if key <= node.key
+      if node.left.nil?
+        node.left = TreeNode.new(key, value)
+        return
+      else
+        add_helper(node.left, key, value)
+      end
+    else
+      if node.right.nil?
+        node.right = TreeNode.new(key, value)
+        return
+      else
+        add_helper(node.right, key, value)
+      end
+    end
   end
 
-  # Time Complexity: 
-  # Space Complexity: 
+  # Time Complexity: O(log n) if balanced; O(n) if not
+  # Space Complexity: O(log n) if balanced; O(n) if not
   def find(key)
-    raise NotImplementedError
+    find_helper(@root, key)
   end
 
-  # Time Complexity: 
-  # Space Complexity: 
+  def find_helper(node, key)
+    if node.nil?
+      return nil
+    elsif key == node.key
+      return node.value
+    elsif key < node.key
+      find_helper(node.left, key)
+    elsif key > node.key
+      find_helper(node.right, key)
+    end
+  end
+
+  # Time Complexity: visit all nodes => O(n)
+  # Space Complexity: array contains all nodes => O(n)
   def inorder
-    raise NotImplementedError
+    return inorder_helper(@root, [])
+  end
+
+  def inorder_helper(node, traversal)
+    return traversal if node.nil?
+
+    inorder_helper(node.left, traversal)
+    traversal << {key: node.key, value: node.value}
+    inorder_helper(node.right, traversal)
   end
 
-  # Time Complexity: 
-  # Space Complexity: 
+  # Time Complexity: O(n)
+  # Space Complexity: O(n)
   def preorder
-    raise NotImplementedError
+    return preorder_helper(@root, [])
+  end
+
+  def preorder_helper(node, traversal)
+    return traversal if node.nil?
+
+    traversal << {key: node.key, value: node.value}
+    preorder_helper(node.left, traversal)
+    preorder_helper(node.right, traversal)
   end
 
-  # Time Complexity: 
-  # Space Complexity: 
+  # Time Complexity: O(n)
+  # Space Complexity: O(n)
   def postorder
-    raise NotImplementedError
+    return postorder_helper(@root, [])
   end
 
-  # Time Complexity: 
-  # Space Complexity: 
+  def postorder_helper(node, traversal)
+    return traversal if node.nil?
+
+    postorder_helper(node.left, traversal)
+    postorder_helper(node.right, traversal)
+    traversal << {key: node.key, value: node.value}
+  end
+
+  # Time Complexity: visit all nodes => O(n)
+  # Space Complexity: O(log n) if balanced; O(n) if not
   def height
-    raise NotImplementedError
+    return height_helper(@root)
+  end
+
+  def height_helper(node)
+    return 0 if node.nil?
+
+    return 1 + [height_helper(node.left), height_helper(node.right)].max
   end
 
   # Optional Method
-  # Time Complexity: 
-  # Space Complexity: 
+  # Time Complexity: O(n^2)
+  # Space Complexity: O(n)
+  # def bfs
+  #   traversal = []
+  #   h = self.height
+  #   i = 1
+  #   while i <= h
+  #     bfs_helper(@root, traversal, i)
+  #     i += 1
+  #   end
+
+  #   return traversal
+  # end
+
+  # def bfs_helper(node, traversal, level)
+  #   return traversal if node.nil?
+    
+  #   if level == 1
+  #     traversal << {key: node.key, value: node.value}
+  #     return traversal
+  #   elsif level > 1
+  #     bfs_helper(node.left, traversal, level - 1)
+  #     bfs_helper(node.right, traversal, level - 1)
+  #   end
+  # end
+  
   def bfs
-    raise NotImplementedError
+    traversal = []
+    return traversal if @root.nil?
+
+    bfs_helper(@root, traversal)
+  end
+
+  def bfs_helper(node, traversal)
+    queue = Queue.new
+    queue.enq(node)
+    while !queue.empty?
+      current_node = queue.deq(node)
+      traversal << {key: current_node.key, value: current_node.value}
+      queue.enq(current_node.left) if current_node.left
+      queue.enq(current_node.right) if current_node.right
+    end
+
+    return traversal
   end
 
   # Useful for printing
diff --git a/test/tree_test.rb b/test/tree_test.rb
index dbf3447..8cba2bd 100644
--- a/test/tree_test.rb
+++ b/test/tree_test.rb
@@ -96,7 +96,7 @@
     end
 
     it "will report the height for a balanced tree" do
-      expect(tree_with_nodes.height).must_equal 3
+      expect(tree_with_nodes.height).must_equal 4
     end
 
     it "will report the height for unbalanced trees" do