While Jehovah's Witnesses obsess over Christmas decor and customs such as trees and mistletoe and giftgiving, etc., none of these things are actually part of "Christmas" itself. Those are mainly secular traditions that differ depending on where you live in the world (and greatly on the hemisphere).
The most startling fact about Christmas is that it is a worship-driven observance which lasts on 16 to 22 days on the Christian calendar (known as the "liturgical calendar") and not 1 day. It is filled with special prayers in the Church marked from the Book of the prophet Isaiah and lasts from the evening of December 24 through Feast of Baptism of Christ, which lands in January either on a Sunday or a weekday, depending on a formula that changes with when Christmas lands.
The only universal custom is Epiphany, marked 12 days from Christmas, the holy day in the church which marks the visit of the magi and lands on January 6th on which homes are usually blessed. This is where the so-called "Twelve Days of Christmas" comes from.
The Christmas tree became popular from Queen Victoria who fell in love with the German custom and introduced it to the public via a Christmas party. She hung the trees upside from the ceiling as decorations.
The introduction of Christmas as a "family" celebration came about through the novella A Christmas Carol written by Charles Dickens who rode on the coatails of the Victorian revival of Christmas in England. Before this the Puritans had banished it due to a hatred for all things they considered Catholic, so when they did pick it back up they instead adopted the Germanic Lutheran customs because they felt "safer" with these.
The Roman Catholic customs were at that time not so much built around Christmas trees as to build a small crèche, a custom introduced by Francis of Assisi to Catholics in 1233. These had become quite ornate by the time the "Victorian Christmas" had been introduced into American society. There were celebrations, but these had moved mostly to Epiphany onward and would become the "Carnival" period leading up to Lent (the "Mardi Gras" once this would become introduced to America).
It is this type of Christmas (the "Victorian") that has become most associated with the 25th of December, commercialized and practiced. It is really not what is religiously celebrated by the Christians in the actual Church. In Spanish countries, fireworks and pinatas are used as Christmas trappings. In Guatamala, they burn a wooden devil in a bonfire on Christmas Eve. And in Italy, instead of Santa delivering presents on Christmas Eve, they have a witch, Befana, who delivers presents on Epiphany Eve, January 5th.
The local customs have nothing to do with the religious observance. They are localized and differ according to place and situation and the comprehension of the people who use the symbols. They are secular trappings and have little or nothing to do with the Nativity of Christ. Anyone can engage in their people's local customs whether they go to a church or mass or not. The religious observances in honor of the Nativity have totally different practices, none of which include Christmas trees, gift giving, parties, etc.