docs(treeview): warning about mixing flat properties with hierarchical data

Author: marin-bratanov

components/treeview/data-binding/overview.md

@@ -58,6 +58,8 @@ Each `TreeViewBinding` tag exposes the following properties that refer to item p
 
 >tip There are default values for the field names. If your model names match the defaults, you don't have to define them in the bindings settings.
 
+>important If you are using hierarchical data binding, your model must not contain a field called `ParentId` (or a field that matches the name given to the `ParentIdField` parameter of a `TreeViewBinding`). That would confuse the treeview that it is binding to flat data, and so there may be no roots and you may see no data.
+
 >caption Default field names for treeview item bindings. If you use these, you don't have to specify them in the `TreeViewBinding` tag explicitly.
 
 ````CSHTML