The old pagan custom of bringing a living tree indoors in the middle of the dark months of the year and decorating it with candles and trinkets was introduced to Britain by Prince Albert, the husband of Queen Victoria. The idea rapidly caught on. Bringing evergreen vegetation in the form of trees, boughs, and branches from the outside to the inside was a magical ritual, a piece of sympathetic magic, meant to encourage the return of spring and the growing season.
The timing of the entrance and exit of the tree was critical. Any time before Christmas Eve was too soon for the tree to come inside, and all decorations had to be taken down and the tree removed by Twelfth Night, January 6. This tradition, however, does not seem to signify for the department stores who start to display artificial Christmas trees from September onwards.
The Christmas tree is traditionally an evergreen tree, usually a spruce or a fir, which is cut down from the forest. The tree itself symbolizes immortality and everlasting life, and the lights draped on it are a reminder that during the darkest time of the year, lighter days are just around the corner. The Yule Celebrations in northern Europe were echoed in similar rituals in southern Europe. The Roman God Atys or Attis was a savior God whose life stary very much parallels that of Christ. Atys was born on December 25 to a virgin mother and was sacrificed to save mankind, killed beneath a conifer, remaining for three days and nights in his tomb before ressurection. His priests, called “dendrophori” (meaning “tree bearers”), were charged with selecting conifers from a sacred grove that would be brought indoors in memory of the death and resurrection of Atys, who is also linked with Apollo, the Sun God.
From the book : The Element Encyclopedia of Secret Signs and Symbols by Adele Nozedar