Hi Laura,
Thank you for contacting Syncfusion Support.
We can select the SubItem of TreeViewItemAdv by setting IsSelected as True. We can scroll the TreeViewAdv by invoke ScrollToBottom, ScrollToTop or ScrollToVerticalOffset method with required offset of scrollbar. We can fetch the Scrollbar from the Template of TreeViewAdv. We have prepared the sample that tries to meet your requirement and you can download the sample from the following link.
Sample Link:
TreeViewAdvsamplePlease let us know if you need further assistance.
Regards,
Berkunath A