There was an episode of Mythbusters where they tested wether they could start any tree fires by putting a crap ton of lights on it and leaving it on for a day. It didn’t work, and even when they used a fully dried out tree it still didn’t work
Is more likely you’ll start a fire with Xmas lights if it shorts out or you overload the socket. So don’t do those things and you should be a-okay. Or just get some nice modern LED lights, they look nice and last forever













