Maria,

             What you say makes perfect sense if you have that many subgroups.  It would be interesting, though far more coding work [which I'm not proposing, by the way], to do something like if there are 5 or fewer subgroups just present them sans the need for a button or link and if more present the link that would reveal them.

              The button, link, alone would be enough to greatly increase general user recognition of the presence/existence of subgroups.  That would be fine as far as I'm concerned.

               Fifty subgroups of a single group suggests to me that you really have more than one group that you're bundling under one very general umbrella group.
--
Brian

A lot of what appears to be progress is just so much technological rococo.  ~ Bill Gray