To check if your Christmas tree lights are working properly, you can use a simple method. First, ensure that all the lights are plugged into the outlet and that the circuit breaker is on. Next, turn on the lights and observe each bulb to see if it's working. If any of the bulbs are not lit, check to see if they have burned out or if they have come loose from the socket. You can also try switching the bulbs out with a spare one to see if that solves the problem. If all the bulbs are working, then the lights should be fine.