I must begin with the disclaimer: I am not an Orthodox Christian. Although I know more about Orthodox than the most westerners do, I do not regard myself as any kind of expert.
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.
My view on the Christmas, as a Marxist-Leninist, is being open-minded towards people having different spiritual values. I believe that spiritual values regarding Christmas is a private matter.