Traditionally, until Christmas Eve (December 24), the Christmas tree will be decorated and then removed after 12 nights (January 6). It is considered unlucky to advance and postpone this date.
However, the modern Christmas shopping season has allowed most stores to set up the Christmas tree at the end of October. (In the UK, Selfridge's Christmas Department opened in early September, including the Christmas tree).
Most American families, habitually erecting a Christmas tree immediately after Thanksgiving (fourth Thursday in November) until the New Year. Some American families did not start erecting the Christmas tree until the second week of December, and the Christmas tree was set up until January 6 (the main festival).
In Germany, the traditional Christmas tree was established on December 24, but some people set it up 1-2 weeks in advance.
In Australia, it was a week before the school summer vacation; except South Australia, where most of it was established in early November (after the Adelaide Credit Union Christmas celebration).