The evergreen fir tree has traditionally been used to celebrate winter festivals (pagan and Christian) for thousands of years. Pagans used branches of it to decorate their homes during the winter solstice, as it made them think of the spring to come. The Romans used Fir Trees to decorate their temples at the festival of Saturnalia. Christians use it as a sign of everlasting life with God.
Nobody is really sure when Fir trees were first used as Christmas trees. It probably began about 1000 years ago in Northern Europe. Many early Christmas Trees seem to have been hung upside down from the ceiling using chains (hung from chandeliers/lighting hooks).