Here's an EXTREMELY cost effective, lightweight and most importantly, SAFE alternative to the above suggestion. For climbing applications, ounce for ounce, there are few things more durable and reliable than quality rappelling rope (I buy mine at REI, but quality rope from any hardware store will work just as well). Here's what you do:
1. Guestimate the diameter of the tree you plan to hunt from.
2. Add 18" to the guesstimate in #1 above.
3. Multiply the answer in #2 by 3.14. This will give you the length of rope you'll need- plus a little extra for tying a few knots- to get around the circumference of the tree.
4. Slide a 12" piece of garden hose over this length of rope. Tie a half-hitch knot in the rope at both ends of the hose. This will prevent the hose from sliding.
5. Create a loop at one end of the rope using a standard bowline knot.
6. Place the rope around the tree passing the end through the loop. Pull snug, BUT NOT TIGHT and secure in place with two half-hitch knots.
NOTE: no spacers are necessary and this rigg will SAFELY anchor your climbing sticks and/or tree stand to the tree as well as ANY chain or cable rigg- but at a fraction of the cost and weight. It is also much quicker to secure to the tree.
Cost? About $2!