To get a Christmas tree in Animal Crossing, you must first visit the Nook's Cranny store in your town. Once you enter the store, you can purchase a variety of decorations and items, including a Christmas tree. Be sure to check the store's inventory regularly, as it changes on a daily basis. Additionally, you can also get a Christmas tree by completing quests or participating in seasonal events. Have fun decorating your tree and celebrating the holidays in Animal Crossing!