How to manually sort rows?
For some reasons, you may not want to rely on the built-in mechanisms to sort rows in a TreeView. For instance, once a sort column ID has been set on a TreeModel implementing the TreeSortable interface, it cannot be returned to the original unsorted state. This may be a problem if you want your users to be able to move rows even in a sorted tree, since it then needs to be unsorted. To manually sort rows, you first need the column headers to be clickable.
