http://www.artisticartifacts.com/ Two lovely young ladies showed us how to make them.
You start by picking out a button and making a loop to hold it with the wire then start with smaller pieces of sweater thread them on the wire add beads on the wire after a few layers - I added some beads but you can't see them. Add more circles of sweaters gradually selecting larger circles. When you have a nice fat tree pick out a spool of thread put the wire through it and the wrap the rest of the wire around the spool and you're done.
Very easy and fun!