Once you have chosen a branch you can wind it with yarn, string or thread. What ever you choose is fine. I chose to use yarn for my entire piece.
Tie the end of the yarn on the closed end of 'V' of the bottom branch. Stretch it up to the top branch and wrap it around once before stretching it to the opposite (top) branch making sure to keep the yarn taunt.
Continue all the way along the branches until you reach the end or where you want to stop.
Tie off the yarn in a knot and trim the extra length with scissors.