Hi Angie,
Thanks for your interest in Syncfusion products.
We have created sample based on your request in which TreeViewAdv is used in DropDownButtonAdv control. TreeViewAdv is added to DropDownMenuGroup and it get displayed while click the DropDownButtonAdv. Please download the sample from the below link.
Please let us know if need further assistance.
Regards,
Jegan Raj M
DropDownButtonAdvSample_1caadb79.zip