Collapsing/expanding sidebar sub-trees?

[Tim Chase]

Is there a way to collapse (and subsequently expand) folders in my
sidebar?

Say I have

  INBOX
    Folder A
      Subfolder A1
      Subfolder A2
    Folder B
      Subfolder B1
      Subfolder B2

is there to navigate to "Folder A" and collapse it so that the
sidebar displays something like

  INBOX
    (+) Folder A
    Folder B
      Subfolder B1
      Subfolder B2

like traditional tree-view controls?

Thanks!

-tkc