If you are getting a real tree this Christmas ... the way to have it stay fresh longer is to drill a 1/4 inch to 1/2 inch hole (determined by how wide the tree stump is - use your judgement) and drill it at least 6-10 inches up the centre of the trunk from the bottom. Then trim at least an inch off the trunk height in order to remove the dried out part.
This helps the tree absorb water easier and will keep it fresh so much longer.