Almost any way imaginable! Pallets, bottle brushes, twigs, wood, what are you looking for?
For small ones you can use pipe cleaners and Garland.
For Large ones you are better off using Solid 12-3 Copper Wire, coiled into a spiral to pull the smallest ring up as the top to add Garland to the entire, tied on with fishing string.
1 pallet can be fashioned into 2 shorter Christmas trees. cut diagonally from one corner to the other. make a trunk and base for each from the rest of the pallet.
Vivian: Here are some fun ideas!
Here is what I did this year for a wood tree