Collapse tree

I tried to search forums, but was unable to find solution, so I put this in feature request. I'd like to have something like "collapse tree" or "collapse drive" button or shortcut. Actually, "collapse drive" function is present in file managers like PowerDesk and Explorer Plus but I found Directory Opus much more powerful and customizeable and I prefer to keep only Directory Opus on my PC. I think "one click" solution instead of lot of clicks to "minus bar" to become to simple tree view could be useful.
I hope everybody will understand what I tried to explain, actually, English is not my native language.
Thanks,
Pavel