Hi Viacheslav,
Thank you for your interest in Syncfusion Products.
To set the vertical scrollbar of the TreeViewAdv, we need to overide the OnRightToLeftChanged event of TreeviewAdv and the set the VScrollBar's RightToLeft property to Yes. To invoke that method we need to set the TreeviewAdv's RightToLeft property to Yes at design time and in FormLoad event we need to change the RightToLeft property to No.
Please refer the below sample that illustrates this:
http://websamples.syncfusion.com/samples/Tools.Windows/F74901/main.htmPlease let me know if any concerns.
Regards,
Fathima