There's some excellent background on this in Fr. Francis X. Weiser, S.J., The Handbook of Christian Feasts and Customs.
I knew Fr. Weiser when he was teaching at the Weston Seminary in Massacusetts back when I was in college. I did a google search and found his book posted on-line:
http://www.neiu.edu/~history/wbook.htm
Fr. Weiser grew up in a little village in Bavaria.
Brilliant co-opting of a pagan symbol:
Evergreen = ever-living
Triangular shape = Holy Trinity
Circular shape = never-ending
My wife having opemed a retail shop recently, it fell upon me to put up a tree this year if we were to have one. In the attic we have enough decorations for a dozen trees as the wife in other times has put up as many as five in our home. I found some strands of plastic clip on candles we last used at least 15 years ago. Needless to say only about half of them lit but being determined , I spent half a day getting them to work. Our tree this year wears only those candles. I am messmerized by its beauty,It is the most wonderous tree we have ever had. But of course I feel that every year. Merry Christmas to all my freepin friends!
Tree lit with candles. Hmmm . . . tree . . . open flames . . . maybe it symbolizes the burning bush of Sinai.
Bottom line: you can fabricate symbolism however you wish. Everyone knows that the "Christmas" tree has its origin in paganism. However, the meaning assigned by pagans has long since been lost and co-opted by the earlier Christian adoption of the tree, along with assignment of different symbolism.
In any event, Freepers, have yourselves a merry little Christmas, give proper honor and worship to the namesake of the holiday, and don't drive yourselves too crazy with the symbolism issues, because there's thousands of years of history and tradition that will mess with your mind if you allow it.