A Christmas tree or Tannenbaum is one of the most popular traditions associated with the celebration of Christmas .
Both setting up and taking down a Christmas tree are associated with specific dates . Traditionally , Christmas trees were not brought in and decorated until Christmas Eve ( 24 December ) or , in the traditions celebrating Christmas Eve rather than on the first of day of Christmas , the 23 December , and then removed the day after twelfth night ( 6 January ) ; to have a tree up before or after these dates was even considered bad luck .