In the fourteenth and fifteenth centuries, pine trees were used in Europe as part of the miracle plays performed in front of cathedrals at Christmas time. The plays detailed the birth and fall of humanity, its salvation through the death and resurrection of Christ and Christ's promise of redemption. The pine trees, decorated with apples, symbolized the Tree of Life in the Garden of Eden.
Though such plays were later banned by the church, the tradition of this Paradise Tree, or Paradeisbaum, was kept alive in individual homes. People began to decorate the tree with wafers to represent the Eucharist; later these wafers evolved into cookies, cakes and fruit.
As early as 1710, German immigrants from the upper Rhine area may have set up the first Christmas tree in the United States, and certainly the custom was strengthened by the wave of German immigration that started around 1830. This German custom in turn probably sprang from two sources: the Paradise trees of the medieval miracle plays, and the decorated wooden pyramid known as the Weihnachtspyramide.
BTW, anyone interested in a PC Christmas Poem?