Saint Nicolas is just one of many characters both real and myth who influenced the current character Santa Claus. Another even older influence is the Norse god Odin, who was known for giving present to believers. He used two ravens to listen in through chimney stacks so he could know who was worthy. The ravens may have later played an influence in the creation of the Christmas Krampus aka Black peter, Santa's demon slave. Which predates the elves which first made an appearance in story in 1850. The Krampus would put naughty children in a sack and carry them off to be his Christmas dinner.
christmass was just being together to celebrate jesus's birth.
Jesus's birth really has nothing to do with the holiday, nor does Christianity for that matter beyond the name and addition of a nativity scene. Originally it was a celebration of the winter solstice. Chritianity co-opted the holiday in order to get the Pagans who celebrated it to convert. The Bible even makes mention of the traditions being pagan and God saying don't do it.
Christmas trees in the Bible.
Jeremiah 10:2- (NIV)
This is what the LORD says: "Do not learn the ways of the nations or be terrified by signs in the sky, though the nations are terrified by them.
For the customs of the peoples are worthless; they cut a tree out of the forest, and a craftsman shapes it with his chisel.
They adorn it with silver and gold; they fasten it with hammer and nails so it will not totter.
Like a scarecrow in a melon patch, their idols cannot speak; they must be carried because they cannot walk. Do not fear them; they can do no harm nor can they do any good."

Christmas, it is the religious holiday most widely celebrated by Atheists.
Us atheists could just start calling what we celebrate Giftmas to celebrate the giving and receiving of gifts and the materialistic nature that the holiday has become.