Hi David,
Thank you for your interest in Syncfusion Products.
The problem is because of the improper usage of BeginUpdate method. When you call the BeginUpdate method it will suspend the painting of control, so the process for expanding the node will not be performed. If you want to suspend the painting on right click then BeginUpdate method should be called after checking the MouseButton.
Please refer the sample from the below link that illustrate this.
Please refer the sample in the link to illustrate this:
rel='nofollow' href="http://websamples.syncfusion.com/samples/Tools.Windows/68830/main.htm">http://websamples.syncfusion.com/samples/Tools.Windows/68830/main.htmPlease let me know if you have any questions.
Regards,
Jisha