Connectable Web Parts

I am trying to implement a simple connectable web part solution -- Provider and Consumer.

There is a drop down list in provider whose selected item's value is supplied to consumer. Consumer once the value is received creates a treeview and adds it to the control tree.

I have the code in consumer's OnPreRender event handler, however, I am not seeing a treeview. What am I doing wrong? I verified that consumer got the value in its prerender event.

Thanks!