how to collape folders in mixer

I've just watched a routing tutorial * which shows a feature to collapse folder tracks in the mixer. In the video the folder tracks have a collapse icon while in my Reaper the onyl show the folder icon without any functionality.

Can I enable this icon? Or is it yet another SWS thingy that would be great if it were in Reaper by default?

Masi

* http://ift.tt/295SrTb

how to collape folders in mixer