As with the other ports to GtkColumnView, this drops the popover and the tooltip.
Connecting to the expanded property (in order to lazy-load children) is a bit weird, but seems to be the only way I could find to do it.

Browsed pidgin.im, double-clicked conference.pidgin.im/clicked the expander, and the rooms were loaded. Double-clicked all the rooms and confirmed the Add Chat dialog was correctly filled. Also clicked the Add button after selecting one and confirmed the same.