by sam marshall.
No it isn't (not without hacks - the OU subpage does this, but it's not a perfect solution and requires code in theme to make it work nicely, which I don't really recommend anyone else to do).
But you might like to look at (& possibly vote for) MDL-37702, which is a proposal I filed to add support for having activities that can contain other activities in a future Moodle version.
--sam