Hi Yi Luo,
Thank you for your interest in Syncfusion products.
To disable the TreeViewItemAdv from expanding on double click, we need to handle the PreviewMouseDoubleClick event. We have prepared a sample in which we have demonstrated the same. Please find the sample attached in the following link.
Sample:
TreeViewAdv_118232.zipPlease let us know if you require further assistance on this.
Regards,
Bharadhi K