The Treeview-widget uses jQuery and since a newer version of the Treeviw-widget, the newest jQuery library doesn't come with the Treeview-widget anymore. What you could do is make sure the newest jQuery library is included. in your project, by adding a line to the head of your index.html:
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
Hope this helps!