I used to wonder about that as a little kid, hearing the stories about how lights on Christmas trees used to be candles. My grandmother even had an antique set of little candle holders for the purpose, not that she used them. I asked her how the Christmas tree didn't burn down. She told me families only lit the candles for a very short time on Christmas Eve as they gathered around the tree to sing.
And that reminds me, I haven't put up my string of LED Christmas lights yet. I'd better get cracking! Since they certainly won't burn anything down. ;-)
Happy holidays!