TreePanel->Tools(Type="Refresh"), when click refresh icon, can I show a mask over the TreePanel?

I put a tools which type is refresh on my treepanel,when I want to reload my treepanel after I updateed the tree data. But now, after click refresh icon, there is nothing mask friendly showed on screen unitil the tree had been updated, can someone tell me how to show a mask over the treepanel at that time.

by the way, can I expand a node which I want to, How?

Thanks

zhang