I mounted mine on the top of a short (6-8") piece of a 4x4 with the top end cut at an angle to point directly at the sun. I personally use a couple of counter-sunk (WAY counter sunk - about 2") wood screws to attach it to the tree because I don't move it often, but the bungee cord method would make this setup pretty mobile.

I also mount mine of the back side of the tree because I like to point the camera to the north to avoid washout shots.