Instead of a real tree, try a tree from recycled cardboard.
"The Cardboard Christmas Tree was designed and developed by Cloud Gate Design LLC, a Chicago based design house. Cloud Gate Design was started in 2006 by two friends, Nick Ng and Dan Greene, as a way to bring their environmentally conscious product alternatives to market.
One of these products is the Cardboard Christmas Tree, which helps extend the life of existing cardboard by using recycled corrugated cardboard for both the tree and its packaging.
In addition, a portion of the profits from the Cardboard Christmas Tree sales are donated to the Arbor Day Foundation's Trees for America program. Through this program, for every one dollar donated one tree will be planted in a damaged forest."