How did the idea of a Christmas tree start?

Its origin is probably within winter celebrations long before the beginning of Christianity. The practice of decorating a tree, or using plants and trees that were green year-round, was important for people in winter climates. Some cultures believed evergreens would keep witches, ghosts, evil spirits, and even illness at bay. During the Middle Ages, December 24 was celebrated as the Feast of Adam and Eve, complete with a Paradise Tree, which was a fir tree hung with red apples. Today, the practice of using decorated evergreen trees as part of the Christian celebration of Christmas is a custom begun in Germany over 400 years ago that spread rapidly throughout northern Europe and, hence, became a tradition transplanted to the New World by European immigrants.