Hi Tomasz,
Thanks for your interest in Syncfusion Products.
We can set the base style to the nodes that are present in the TreeViewAdv. Please check with the sample for more clarification.
[Sample Link]
http://www.syncfusion.com/uploads/redirect.aspx?file=CS_ad8c5b1.zip&team=development[User Guide]
http://help.syncfusion.com/ug_91/User%20Interface/Windows%20Forms/Tools/Documents/nodespecificstyle.htmPlease let us know if you have any concern.
Regards,
J Jeraldes