Hi Richard,
We don’t have support to persist to order the TreeViewItems in source level, we can provide the workaround to achieve the expected behavior in sample level. However, if you are interested in receiving the workaround for the query, then, we would request you to use our Direct-Trac Support system to resolve all your technical queries.
For more details, please login into http://www.syncfusion.com/Account/ and we will be happy to help you.
Please let us know if you have any queries.
Regards,
Karthikeyan