I thought this, too, so I did a little research. Turns out that during the reign of the Roman Empire (which was Pagan), something-or-other was being celebrated by Pagans, so Christians decided to celebrate something during this time of year as well. The same thing happened with Easter, except we kept the name of the Pagan goddess in the title. There are still elements of Christmas that most Christians do not realize are of Pagan origin, such as Yule (which isn't really common anymore) and Mistle-toe.
No, celebration of Christmas is
not found in the Bible. I am assuming you are referring to Jer. 10:3-5, which states (NIV) - "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."
It is referring to an ancient Pagan worship practice where Pagans would cut a tree out of the forest, fasten it in place, and chisel it into an idol, and cover it with gold and such. And no, use of the Christmas tree did not originate with Martin Luther, either. The first record of decorating a Christmas tree is traced back to Germany in 1521. There is no evidence to support that Martin Luther was the first to use it.
So, that's my history lesson for the day.
[edit:
Here's a site, complete with quite a fair share of references.]