Actually a nice Nativity scene would be better than a Christmas tree.
A Catholic protest group set one up there... http://www.lifesite.net/ldn/2006/dec/06121503.html
Decorated trees are nice. Wouldn't mind seeing them all winter long. I like the lights they string up here in Edinburgh.
I always found the nativity scene creepy and strange. Don't see why it needs to be in a public place.