Slightly-belated Christmas joke--this explains the tradition of there being an angel on top of a Christmas tree.
Decades ago, Santa Claus was having a terrible holiday season:
Mrs. Claus, normally his greatest support, was going through 'change of life' (menopause) and was an emotional wreck--she was either complaining bitterly about living at the North Pole, or crying uncontrollably while sobbing that her life had been ruined.
One-third of the elves had gone on a 'wildcat' strike and were picketing his workshop, forcing the other elves, and Santa himself, to work longer and harder, which the non-striking elves resented.
Worst of all, the reindeer had all caught some sort of flu-like 'bug,' resulting in attacks of copious diarrhea, which Santa himself (the stable elves being among the strikers) had to shovel out of their stalls several times a day.
God looked down on the North Pole and realized that Santa wouldn't be able to put up and decorate a Christmas tree that year, as he and the non-striking elves were too exhausted and his wife was emotionally dysfunctional, so He had his angels decorate a beautiful tree. He then summoned a very peppy, Pollyanna-type female angel and told her to deliver the tree to Santa's residence.
God told the pretty, young-looking angel, "Santa's under a lot of stress, so I want you to take the tree to him, ask him where he'd like it to go and put it there--no arguments, no suggestions, no discussion, just do whatever he wishes regarding the tree's location."
The perky angel nodded. "Got it, Boss--whatever Santa says."
Santa was in the stables, grunting and sweating as he shoveled foul-smelling reindeer diarrhea, when the beaming, bouncy-looking angel showed up carrying the beautifully-decorated tree.
"I've got your Christmas tree here, Santa," she enthused brightly, "What do you want me to do with it?"
Which is why there's always an angel on top of a Christmas tree...

--C.K.