It's probably a piece of driftwood that looks like a tree that was decorated with some kind of moss. Christmas Moss, probably.
Actually, yes it should be simple to make in the home aquarium. Most real driftwood isn't too expensive, here's a couple sites for real driftwood: http://www.aquabid.com/cgi-bin/auction/auction.cgi?driftwood
http://www.drsfostersmith.com/product/pet_supplies.cfm?c=3578+6635+12162
http://www.thatpetplace.com/pet/cat/infoL3/22962/category.web
Find some moss that you can easily attach to the driftwood: http://www.aquabid.com/cgi-bin/auction/auction.cgi?liveplantsm
Then attach it with a rubber band and eventually it will root and you'll have a bonsai tree in your aquarium
E-mail me for any questions!
ZTM