diff --git a/trees/bt_height.py b/trees/bt_height.py
index 32fbc7d..b10b178 100644
--- a/trees/bt_height.py
+++ b/trees/bt_height.py
@@ -5,7 +5,7 @@
 
 def height(root):
       
-      if not root:
+      if root is None:
             return 0
             
       return 1 + max(height(root.left), height(root.right))