Hi Mike,
Thanks for using syncfusion products.
Yes, there is a way to expand/ collapse all root nodes in TreeViewAdv. We have prepared the small workaround sample to illustrate this. We have used "IsExpanded" propery to achieve this requirement in TreeViewAdv. We hope it would satisfy your needs.
Please let us know if you have any queries.
Regards,
David C
TileViewExpand_CollapseAll_c22181b.zip