When you buy a living Christmas tree, the longest you should keep it inside is about ten days or less. If you want to get one earlier, keep it outside near the front door for a few days to be festive, this will help raise its survival rate for later.
After Christmas, place it outside in a shady position for a week, then move it into the morning sun and sheltered from the afternoon heat for a week. After that, it should be fine to go outside permanently. Water the tree well, without a saucer present, as pooling water at the bottom of the pot can lead to root rot. The water should freely drain out. If possible, take the tree outside in a shady spot, to water in the morning before going out, and move it back in when you get home.
When taking it back outdoors give it a drink once a week with SeaMax Seaweed to help it restart. Keep this up over the coming month to reinvigorate the tree. If you plant it in the garden, add 90ml or two caps of Liquid Seaweed to 9L of water in a watering can and water the tree once planted to settle it into the new home. Repeat liquid feeding fortnightly for six weeks.