Tinsel for decoration started off as shredded silver strands, but silver tarnishes quickly. And these days, it’s rather expensive.
So, people switched to copper, but wartime restrictions meant that people needed to use another metal.
That’s around when aluminum became cheap and easy to use, but aluminized paper is a fire hazard, and the lights on trees would heat up the paper and burn houses down.
Lead is nice and shiny. And toxic. It causes brain damage. But if your kid sucks on Christmas tree decorations and thinks some fat dude’s bringing presents, really, how much stupider can they get?