The process of replanting a Christmas tree involves several steps. First, you will need to dig up the tree's root ball and place it in a pot filled with a mixture of potting soil and compost. Make sure the tree is positioned so that the root ball is level with the soil. Next, cover the root ball with soil, leaving the top of the tree exposed. Water the tree regularly, and keep it in a sunny spot until it's ready to be replanted outdoors.