The traditional time to put up a Christmas tree is on the first Sunday in December, which marks the beginning of the Christmas season. However, there is no hard and fast rule for when to put up a Christmas tree, and people can choose to put up their trees whenever they feel ready to do so. Some people may choose to put up their trees earlier in the season, while others may wait until closer to Christmas. Ultimately, it's a matter of personal preference and how you want to celebrate the holiday season.