Start with tomato cages. I bought all of these at home depot for about $2.80 each. They were the larger 4 tier ones.
Then we started by bending down the points. This was a team effort. The purpose for this was to give a place on top of the tree to add the bow. It would just sit in the middle of the bent wire.
Then we found some garland at wal mart $4 for 9 ft. Later I found some for $2 for 9ft but it wasn't as thick. I bought it later and used and it worked fine though.
Start at the bottom and work your way up. We wrapped the garland around the outside of the straight sides and then every once in a while wrapped it around the round layers to hold it in place. Once you get to the top you can just cut the excess garland off with wire cutters.
They work perfect in kids rooms. As soon as we got home the kids each picked a tree and took it in their rooms to decorate. A strand of 100 lights filled the trees perfectly. I had other ideas for the trees but the kids were so excited about them that I just let them have them and decorate them how they wish. I had bought some pretty Christmas ribbon for a bow, some berry garland and red beaded garland but oh well.
Sorry for the bad photos.