This is certainly not an original idea. I have seen the idea of making your own crayons a bunch of times over the years. It has always been one of those project ~ See more about party favors, homemade crayons and crayons.
Not just for hanging the Christmas tree.... Hang them on a tree branch, use as present adornments, napkin rings, put around candlesticks, add to your wreaths, adorn a wine bottle, place them in a pretty bowl, party favors...so many possibilities!