Please see the video tutorial for option #1 or option #2 for adding on an ornament hanger.
Written instructions are for option #1 and pictured is option #2.
Cut a long piece of thread, yarn, or twine. Insert the fiber into a yarn/darning needle and double knot one end.
Insert the needle through the middle of the large tree (from inside - out), so the knot is on the inside of the tree.
Insert needle through the middle of the medium tree and then the small tree (from inside - out).
Cut the twine so you can take the needle off and make a knot.
Tip: If you're going to be selling or gifting these trees, it would be best to put a dab of fabric glue on the inside of the large tree to keep the knot in place.
You can also put a dab of glue on the first two rounds before placing the tree layers on top of each other.