Update app.py

app.py

@@ -88,7 +88,7 @@ ROOT = None
 def create_binary_tree_edges(root):
     edges = []
     prev = [root]
-    while len(prev) == 0:
+    while len(prev) > 0:
         new_prev = []
         for node in prev:
             edges += [(node.id, child.id) for child in node.children]