Christmas is a time of traditions. If you have found time in the rush before Christmas to decorate a tree, you are sharing in a relatively new tradition. Although the Christmas tree has ancient roots, at the beginning of the 20th century only 1 in 5 American families put up a tree. It was 1920 before the Christmas tree became the hallmark of the season. Calvin Coolidge was the first President to light a national Christmas tree on the White House lawn.