The left sidebar allows you to move devices from the right sidebar - there are a few uses:
* Present a sidebar on the left, rather than right, if you (or your users) prefer it there * Split devices between left and right, so that more devices can be seen without scrolling * Split devices between left and right, so that like data fields can be grouped together etc.
There is no way, at present, or customising the device types beyond their standard nature - so there is no means of creating a hierarchical view as you suggest... at least not yet :)