Santa went out to load his sleigh with the big bag of toys and the bottom fell out of the bag, so after spending half an hour picking toys out of the snow, he had to hunt around under the stairs for another bag, burnt his fingers on the match he was using to see with and bumped his head!
Santa went out to the shed getting more upset every minute, to find four reindeers sick and that he'd have to make do with only two. As he was putting the harness on them, one of them kicked him in the stomach and knocked him on his butt onto a fresh pile of reindeer manure, wrecked his only clean suit and broke the harness!
While Santa was sitting around in his shorts, waiting for his suit to dry and sewing the harness, the door bell rang and scared the mess out of him and he jabbed the needle right though his thumb, tripped over the coffee table and stubbed his toe on the chair! He finally got the door open to find standing there, the Angel who had come to deliver the Christmas tree.
The Angel asked him, "So where do you want me to put the tree?" And that is the story of how the Angel came to be on top of the Christmas tree.