diff --git a/lib/tree.rb b/lib/tree.rb
index c0d4b51..d60e72b 100644
--- a/lib/tree.rb
+++ b/lib/tree.rb
@@ -16,40 +16,94 @@ def initialize
     @root = nil
   end
 
-  # Time Complexity: 
-  # Space Complexity: 
+  # Time Complexity: O(log n)
+  # Space Complexity: O(1)
   def add(key, value)
-    raise NotImplementedError
+      # raise NotImplementedError
+    # if the root is nil set the root to be a new node with the given value and return the node.
+    return @root = TreeNode.new(key, value) if @root.nil?
+    current = @root
+    while current != nil 
+      if key <= current.key 
+        if current.left.nil?
+          current.left = TreeNode.new(key, value)
+          return
+        end
+        current = current.left
+      else
+        if current.right.nil?
+          current.right = TreeNode.new(key, value)
+          return
+        end
+        current = current.right
+      end
+    end
   end
 
-  # Time Complexity: 
-  # Space Complexity: 
+  # Time Complexity:  O(log n)
+  # Space Complexity: O(1)
   def find(key)
-    raise NotImplementedError
+    return nil if @root.nil?
+    current = @root
+    while current != nil
+      if key == current.key
+        return current.value
+      elsif key > current.key 
+        current = current.right
+      else
+        current = current.left
+      end
+    end
   end
 
-  # Time Complexity: 
-  # Space Complexity: 
-  def inorder
-    raise NotImplementedError
+  # Time Complexity: O(n)
+  # Space Complexity: O(n)
+  
+  def inorder(current = @root, array = [])
+    # traverse the left subtree
+    # visit the current node
+    # traverse the right subtree
+    return array if current.nil?
+    inorder(current.left, array)
+    array << { key: current.key, value: current.value }
+    inorder(current.right, array)
+    
   end
-
-  # Time Complexity: 
-  # Space Complexity: 
-  def preorder
-    raise NotImplementedError
+  
+  # Time Complexity: O(n)
+  # Space Complexity: O(n)
+  def preorder(current = @root, array = [])
+    # visit the current node
+    # traverse the left subtree
+    # traverse the right subtree
+    return array if current.nil?
+    array << { key: current.key, value: current.value }
+    preorder(current.left, array)
+    preorder(current.right, array) 
   end
 
-  # Time Complexity: 
-  # Space Complexity: 
-  def postorder
-    raise NotImplementedError
+  # Time Complexity: O(n)
+  # Space Complexity: O(n)
+    
+  def postorder(current = @root, array = [])
+    # traverse the left subtree
+    # traverse the right subtree
+    # visit the current node
+    return array if current.nil?
+    postorder(current.left, array)
+    postorder(current.right, array)
+    array << { key: current.key, value: current.value }  
   end
-
-  # Time Complexity: 
-  # Space Complexity: 
-  def height
-    raise NotImplementedError
+  
+  # Time Complexity: O(n)
+  # Space Complexity: O(n)
+  def height(current = @root)
+    # If the current node is nil return 0
+    # Otherwise return 1 plus the maximum of the heights of the right and left subtrees
+    return 0 if current.nil?
+    left = height(current.left)
+    right = height(current.right)
+    left >= right ? 1 + left : 1 + right 
   end
 
   # Optional Method