Not sure that we have a column suitable for sortChildren. I am with bitmap in principle (particularly since I think the GUI is updated by default for each call to addChild - but do we have a throttle on it already?).

Since we know that QT (currently) adds a list in reverse order, we could possibly switch from a List to a Queue and insert new items at the beginning in order to generate the list in reverse order.

BUT... the problem of adding a list in one call is that, unless the call is specific about the sequence in which items from the list are added, then it is implementation dependent and could change unexpectedly.  The Qt documentation for addChildren (http://qt-project.org/doc/qt-4.8/qtreewidgetitem.html#addChildren) doesn't explicitly say, though could possibly assume it was implied that it would be in the same sequence - but in practice in PyQt it isn't . So, IF the order that files appear in Unmatched Files and in a Cluster is important, then to avoid implementation issues, this is the only way to do it.

I guess we could wrap the loop in code which prevents the GUI being updated for the album - which would help with performance.