From the BBC:
According to one legend the famous Devon Saint, St Boniface, was the creator of the very first Christmas tree. In the early part of the 8th century, St Boniface was sent into Germany as a missionary, with an aim of converting the pagans to Christianity. St Boniface was later to become the patron saint of brewers, so sending him to beer loving Germany may well have been a masterful mission. He worked tirelessly in the country destroying idols and pagan temples across Germany and building churches in their place. He was named Archbishop of Mainz and founded or restored the diocese of Bavaria. It was on this trip, around the time of Winter Solstice, that he was said to have come across a group of pagans worshipping an old oak tree. Horrified by what he saw as blasphemy, the all-action St Boniface grabbed the nearest axe and hacked down the tree. As he did this he called to the pagans to see the power of his God over theirs. Pagan feelings were understandably mixed, but Boniface’s actions were obviously taken in good spirit, with some of the tales saying he converted the pagans on the spot. This is where the tale now divides. Some say St Boniface planted a fir tree there, but the most common idea is that a fir tree grew spontaneously in the oak’s place. The fir was seen as an image of God and many believed its evergreen symbolised the everlasting love of the Maker. According to the myth, the next year all the pagans in the area had been converted to Christianity and hung decorations from the tree to celebrate what they now called Christmas rather than Winter Solstice. The legend spread and soon Christmas trees became the norm in the newly converted Bavaria, and then spread out to become the tinsel strewn, electric lit, bauble hung festival we know today.