I've heard of some species being able to grow roots even if they've been cut, but most cut Christmas trees are not going to do so. It's important to keep the tree well-watered and to make sure it has enough light so that it can stay healthy and vibrant throughout the season. But once the holidays are over and you're ready to get rid of the tree, it's best to take it to a composting facility so that its nutrients can be recycled back into the soil.