You do not tie yourself to the tree. The best way is to hook your safety harness or vest to a line attached to the tree your stand is on, then hook the short line from your vest or harness to the prusik knot tied to your drop line you tied to the tree. I would use a bowline knot to tie to the tree, it is strong and easily untied. There are other knots you could use. Read and look at this.

http://www.wideopenspaces.com/how-to...d-safety-line/