Yes, it is generally safe to leave Christmas tree lights on, as long as you follow a few precautions. Make sure to use lights that have been approved by a recognized testing laboratory, such as UL or ETL. Also, make sure to inspect your lights for any damage or fraying before using them, and don't overload the outlet with too many lights. With a little bit of caution, you can keep your tree lit and festive throughout the holiday season!