If you are planning on getting a cut Christmas tree, consider treating them like a cut flower to keep them healthier for longer. Before bringing your tree indoors, make a fresh cut about one inch from the base then immediately submerge it in fresh water. No need to add a preservative, just don’t let the reservoir in the tree stand run out of water.  Christmas trees will ‘drink’ heavily for first few days. Eventually they will dry out, just like a cut flower, but this method will encourage them to survive for longer.