One User Control Has Datalist row Command Need to load another User Control in asp.net using vb.net

let say i have Two user control  U1 and U2.
I have a treeview control T1
U1 include a one datalist.
U2 include a one datalist.
I Place a U1 in a aspx file call home.aspx where i use a placeholder for dynamicly load user control.
t1 is a treeview for menu so when i click on a parent item i load u1 in placeholder and
when i click a child node in t1 then i can load u2 in place holder.
Here u1 content parent data like product category.
U2 content child data like product sub category.
click t1 parent node load u1 and child node load u2 ok.
but if a user click on u1 dataitem it also need to laod u2 and unload u1.
can it be possible?
or if anyone can guid me how to use single page with multiple user control response each other event.
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