If your harness is set up for it, there will be two loops, one on each hip. Put a carabeier on each loop and use a linemans belt or a climbing rope that has a loop tied on one end and a sliding prusik knot to wrap around the tree and hook to the carabiners. This will hold you securely hold you to the tree, hands free. Here are some pics that might help.
On the left is what the rope set up would look like in use.
The middle left is a carabiner(just so ya know or in case ya called it something else)
The middle right is what a sliding prusik knot will look like. That should be on a rope that has a very tightly tied loop on one end, and a knot on the other to keep from slipping off.
And the right is a linemans belt set up in us, you can get an idea of how you will be hanging off the tree .
Heres a link where you can but all of the above or just take a better look at them. Good luck and be safe.
http://www.huntersafetysystem.com/st...cessories.html