The amount of time you should leave your Christmas tree up depends on a few factors. If you have a real tree, it is recommended to keep it up for no more than two weeks. If you have an artificial tree, you can leave it up as long as you'd like. However, it's important to keep in mind that keeping your tree up for too long can cause it to become dusty and brittle, which can be a fire hazard. So it's best to take it down as soon as possible after the holidays.