diff --git a/lib/tree.rb b/lib/tree.rb
index c0d4b51..17195e1 100644
--- a/lib/tree.rb
+++ b/lib/tree.rb
@@ -16,47 +16,124 @@ def initialize
     @root = nil
   end
 
-  # Time Complexity: 
-  # Space Complexity: 
-  def add(key, value)
-    raise NotImplementedError
+  # Time Complexity: o(n) or (log n)?
+  # Space Complexity: o(n)
+  def add(key, value = '')
+    node = TreeNode.new(key, value)
+    current_node = root
+    if root.nil? 
+      @root = node
+    else
+      # if true, new node is going to right of root
+      while current_node
+        if key > current_node.key
+          if current_node.right.nil?
+            current_node.right = node
+            return
+          end
+          current_node = current_node.right
+        else
+          # new node is going to the left of root
+          if current_node.left.nil?
+            current_node.left = node
+            return
+          end
+          current_node = current_node.left
+        end
+      end
+    end
   end
 
-  # Time Complexity: 
-  # Space Complexity: 
+  # Time Complexity: o(n) or (log n)?
+  # Space Complexity: o(n)
   def find(key)
-    raise NotImplementedError
+    current_node = @root
+    return nil if current_node == nil
+
+    while current_node != nil
+      if key < current_node.key
+        current_node = current_node.left
+      elsif key > current_node.key
+        current_node = current_node.right
+      else
+        return current_node.value
+      end
+    end
+
+    return nil 
+
   end
 
-  # Time Complexity: 
-  # Space Complexity: 
+  # Time Complexity: o(n)
+  # Space Complexity: o(n)
   def inorder
-    raise NotImplementedError
+    return [] if @root.nil?
+    return inorder_helper(@root)
   end
 
-  # Time Complexity: 
-  # Space Complexity: 
+  def inorder_helper(node)
+    tree = []
+    tree += inorder_helper(node.left) if node.left
+    tree << {key: node.key, value: node.value}
+    tree += inorder_helper(node.right) if node.right
+    
+    return tree
+
+  end
+  # Time Complexity: o(n)
+  # Space Complexity: o(n)
   def preorder
-    raise NotImplementedError
+    return [] if @root.nil?
+    return preorder_helper(@root)
+
   end
 
-  # Time Complexity: 
-  # Space Complexity: 
+  def preorder_helper(node)
+    tree = []
+    tree << {key: node.key, value: node.value}
+    tree += preorder_helper(node.left) if node.left
+    tree += preorder_helper(node.right) if node.right
+    return tree
+  end
+
+  # Time Complexity: o(n)
+  # Space Complexity: o(n)
   def postorder
-    raise NotImplementedError
+    return [] if @root.nil?
+    return postorder_helper(@root)
   end
 
-  # Time Complexity: 
-  # Space Complexity: 
-  def height
-    raise NotImplementedError
+  def postorder_helper(node)
+    tree = []
+    tree += postorder_helper(node.left) if node.left
+    tree += postorder_helper(node.right) if node.right
+    tree << {key: node.key, value: node.value}
+
+    return tree
+  end
+
+  # Time Complexity: O(n)
+  # Space Complexity: o(n)
+  def height   # somewhere between log_2(N+1) and N
+    return 0 if @root.nil?
+    return height_helper(@root)
+  end
+
+  def height_helper(node)
+    return 0 if node.nil?
+    count = 1
+    left_height = height_helper(node.left)
+    right_height = height_helper(node.right)
+    count += [right_height,left_height].max
+    return count 
   end
 
   # Optional Method
   # Time Complexity: 
   # Space Complexity: 
   def bfs
-    raise NotImplementedError
+    return [] if @root.nil?
+    # raise NotImplementedError
   end
 
   # Useful for printing