The best way to keep a Christmas tree hydrated is to make sure that it has plenty of water. You can use plain water or add a drop of pine oil to the water to help it smell nice. It is also important to check the water level regularly and add more as needed. You should also make sure that your tree is not in direct sunlight or near a heat source, as this can cause it to dry out quicker. Finally, remember to keep the tree away from any open flames or heaters.