I usually use a mixture of water and a small amount of plant food. The plant food helps to keep the tree hydrated and nourished, ensuring that it stays healthy and green throughout the holiday season. I also try to keep the water level high, so that the tree has plenty of moisture to absorb. This is especially important if you have a live tree, as it will need more frequent watering than an artificial one. Finally, I make sure to keep the water fresh and clean, changing it out every few days or so to prevent the buildup of bacteria and other microbes.