Suggestion;
Go to your local home depot, or lowes, and pick up a roofing harness.

-It has an anchor that you screw to the top of the roof that is fully adjustable for the pitch of the roof. In this case, a Tree.

-The harness is a four point shoulder and legs, and has a clip on it for the rope. when you set your stand, simply screw the anchor into the tree above your stand

-clip the rope on, letting the rope down to the ground.

-when you arrive at your stand with the harness on your body, clip the slide on the rope to your back and start climbing. you can only go up at this point, unless you take the rope in your hands and manually move the slide down the rope.

If you fall, there is a six-foot extention in the rope that releases to cushion you from when your slide locks and stops you on your way to the ground.

Price; 90-250 bucks depending on comfort of the harness.

It is OSHA approved for climbing all over roofs of any angle, at any height.

this one is 130 bucks and is the one I use in treestands and on roofs.