Setting up a Christmas tree in the yard or home and decorating it is a part of tradition in celebrating Christmas. Earlier real evergreen conifer trees were cut and brought to homes to put as a Christmas tree. Now artificial trees are also used widely as cutting down trees for decorating can have huge environmental impacts. Even though artificial trees are widely used there are still farming of Christmas trees for the Christmas season and there are many who follow the tradition of set up real evergreen trees in their homes during Christmas period.
Trees like fir, spruce or pine are used generally as Christmas trees. There are also many other trees used as Christmas trees in different parts of the world.
The Christmas tree is decorated by floating lights around it, hanging ornaments, baubles to it. In Denmark there exists a tradition in which on people circle around the Christmas tree joining the hands and dance singing traditional Christmas songs. Read about Danish Christmas traditions here
Setting up of evergreen trees in homes for celebrating winter festivals was a part of pagan worship. Romans had this tradition of decorating their homes with evergreen trees or branches at the time of their solstice celebration. The tradition was then adopted by Christian believers of Europe and it later became a tradition associated with Christmas worldwide.