add note for multiple treeview's

docs/javascript/treeview.md

@@ -51,6 +51,14 @@ $('ul').Treeview(options)
 > ```
 {: .quote-info}
 
+> ##### IMPORTANT!
+> If you want to use a multiple treeview's beside the main-sidebar treeview, 
+> then you need to add to all treeview's a ID-tag.
+> ```html
+> <ul data-widget="treeview" id="someIdNameOrSo" data-accordion="false">...</ul>
+> ```
+{: .quote-danger}
+
 ##### Events
 {: .mt-4}