Make your own rock look like a tree and stick that in the middle of a cube, any size. Have GSP or similar green coral, algae, etc cover the top to look leaves.
You could make the tree hollow and make holes look like knots for the fish to swim thru.
Or even better, have the overflow run down the middle so you don't see any equipment in the tank.
Holy crap, I just got really excited over this idea
. I'm doing it! Well when I have time and money, lol (I can hope!)