You may find this video
by CreativeKayt a member (check out her other videos too - very informative.
BTW, I made a pair of tree straps by hand stitching with upholstery thread and a large doll needle. I used a back stitch in a sort of zig zag pattern, going back and forth three or four times, with strong bar tacks on each end. I made a total of five lines, and the result is very strong.
That said, I also ordered a pair from Arrowhead Equipment - Paul's straps are much lighter and neater than my hand stitched creations, and reasonably priced too