As long as it is working, any idea is good. I like the approach.

If you want to use the WARP standard approach, you can use the client-side refresh() method of the WARP - it automatically refreshes the WARP panel and all controls inside it.

More info on WARP client side object model can be found in the online help (the last link from the navigation left)

http://help.infragistics.com/NetAdvantage/NET/2008.2/CLR2.0/ 

but it is not partial post back, it's full postback, however because I already wrap it in WARP, the screen didn't flick.

 I have wrap other tree in WARP to, so if i want to do postback i trigger it from client, by the way, i am using frame, each frame has only 1 tree, so if i do postback didn't affect other component :P

I realize that my ideas maybe not too good, because I'm not using full advantage of WARP

 since i already half way, it's little late to modif my code again T_T, i'll try WARP after i finish the design and functionality first, thx for the hint :)

You could also put TreeB in a Web Aysnc Refresh Panel (WARP Panel) and on the node click event of Tree A you could set a hidden variable perhaps in the panel and then tell it to refresh and populate treeB that way. You can also tell the WARP panel to handle a control's postback events, so the onclick of TreeA could fire the WARP Panel and treeB can be populated that way...

 hallo carlos,

 the data is not loaded yet in the page, it loads when node in treeA clicked, thx for the hint i also thinking of that possibility but i am still not sure whether can fill the treeB.

however to quit the hustle bustle i decided to use frame so treeA and treeB is in different frame, it makes it simpler thanks for your help :)