diff --git a/line.py b/line.py
index bfece53..6d04217 100644
--- a/line.py
+++ b/line.py
@@ -216,6 +216,13 @@ class Line(SecondCurrencyMixin, Workflow, ModelSQL, ModelView):
                 },
             })
 
+    @classmethod
+    def view_attributes(cls):
+        return super().view_attributes() + [
+            ('/tree', 'visual',
+                If(Eval('balance', 0) < 0, 'warning', '')),
+            ]
+
     @classmethod
     def migrate_amount_2nd_currency(cls):
         """ add amount-2nd-currency