Rothco Commando Wire Saw with Nylon Hand Straps, 'strongest wire saw anywhere', 48 kilo breaking strain, wrist loops add comfort and enables longer use, cuts wood, plastic bone, etc.
Find a branch or stick that is roughly 1.5 times the length of the wire saw. Next, cut a thin notch in each end of branch and insert saw.
Attach a piece of rope to each end of saw. Throw one end of the rope over the branch you wish to cut.