It would seem that the greenest way to enjoy a Christmas tree is to buy a live tree to replant when the holiday has passed. However, there are numerous things to consider when exploring this option. Since trees are dormant in the winter, live trees can stay no more than a week indoors or they will wake up and begin to grow again in the warmth. If this happens there is a good chance the tree will not survive once it is returned to the cold winter outdoors.
It also needs gradual transition to the interior climate, and then again when it goes back outside. If you live in a climate where the ground will be frozen, you need to pre-dig a hole for the tree before the ground freezes. You also need to research what type of tree will do well with your soil and climate. See these tips for buying and caring for a live tree .