diff --git a/pydal/objects.py b/pydal/objects.py
index a27bb0ad4..e29559ba4 100644
--- a/pydal/objects.py
+++ b/pydal/objects.py
@@ -3000,7 +3000,7 @@ def as_trees(self, parent_name="parent_id", children_name="children", render=Fal
             row[children_name] = []
         for row in rows:
             parent = row[parent_name]
-            if parent is None:
+            if parent not in drows:
                 roots.append(row)
             else:
                 drows[parent][children_name].append(row)