--- a/svghmi/ui.py	Fri Nov 24 23:56:38 2023 +0100
+++ b/svghmi/ui.py	Sat Nov 25 00:18:05 2023 +0100
@@ -717,7 +717,8 @@
         register_for_HMI_tree_updates(weakref.ref(self))
 
     def HMITreeUpdate(self, hmi_tree_root):
-        self.SelectionTree.MakeTree(hmi_tree_root)
+        if self:
+            self.SelectionTree.MakeTree(hmi_tree_root)
 
     def OnHMITreeNodeSelection(self, hmitree_nodes):
         self.Staging.OnHMITreeNodeSelection(hmitree_nodes)