>As soon as I click on any of the Plus I get the full TV of the clicked Forum.

Even by doing such layout, I wouldn't be able to provide in one click the full treeview of the clicked forum as you could end up with thousands of messages, which wouldn't make sense. This is why the treeview turns dynamic when there is a need for it, as per the parameter in your account setup for the minimum messages before the treeview goes dynamic. The values are from 50 to 1000 with the default value of 400.

I wouldn't develop anything on that, even assuming you would want level 2 and 3 to not appear at first. I believe what we have now suits the general public very well and I wouldn't want to overcharge that functionality with something that is already working well.