Having the whole gallery menu expanded by default is also an idea. However, that wouldn't let the user to choose if he/she wants to have it expanded. That's why I was thinking of letting the user choose to either expand the whole menu with one click if the user wants to and click again to shrink it. How about making it possible to do both those things from the admin panel? Since I can still understand if some or even many users prefer to have it whole expanded by default. - Then the user doesn't have to expand it.
Some users may think that a menu with really many nodes might look a bit cluttering when all is expanded, while others don't and instead find it useful. So thats why I think the user could also be possible to choose.
Having an menu item for the user to click on to expand the whole menu is maybe not the most effective and attractive way to do it though.. thats why I am open for suggestions
Maybe have a expand button just below 'Home'? Like '[+] Expand Menu' and when expanded this appears instead '[-] Shrink Menu'