Hi Sam,
Thank you for your interest in Syncfusion Products.
We can replace the standard +/- signs for the expand/collapse buttons in the TreeViewAdv with the custom images by setting ImageList to the NodeStateImageList property of the TreeViewAdv. By setting DefaultCollapseImageIndex and DefaultExpandImageIndex properties all the ParentNode can be displayed with default images for expanding and collapsing actions. Kindly refer to the KB given below that illustrates this:
http://www.syncfusion.com/support/kb/tools/Default.aspx?ToDo=view&questId=403Please let me know if any concerns.
Regards,
Fathima