From the eleventh Century, religious plays called "Mystery Plays" including the popular Paradise Play depicting the story of the creation of Adam and Eve, their sin and banishment from Eden. An evergreen tree was the logical choice for a lush garden tree on this winter festival, and it was decorated with apples symbolizing the forbidden fruit It ended with the promise of the coming Savior and his incarnation, so gradually flat wafers symbolizing the forgiveness of sins in communion were added to the paradise tree, making it now not just the tree of knowledge but also the tree of life. This resulted in a very old European custom of decorating a fir tree in the home with apples and small white wafers representing the Holy Eucharist at Christmas time. These wafers were later replaced by little pieces of pastry cut in the shapes of stars, angels, hearts, flowers, and bells. In some areas the custom was still to hang the tree upside down.

In addition to the paradise tree, many German Christians set up a Christmas Pyramid called a Lichstock - a open wooden frame with shelves for figurines of the Nativity covered with evergreen branches and decorated with candy, pastry, candles, and a star. The star of course was the star of Bethlehem, the candles represented the light of Christ coming into the world, the evergreens were the symbol of eternal life, and the candy, fruits, and pastries, the goodness of our life in Christ, the fruits of the spirit, etc. By the seventeenth century the Lichstock and the "Paradise Tree" became merged into the modern Christmas tree.

Source: http://www.eldrbarry.net/mous/saint/xmastree.htm

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