According to the book, The Chalice and the Blade by Riane Eisler, "The time for Christmas....was chosen because this was the time of year when the ancients traditionally celebrated the winter solstice." (There are about 35 pages of footnotes in the book for those who are interested.) The tree may have many origins (check out factmonster.com), but most likely was brought into Christianity in the 8th century by St. Boniface. It's a symbol that those of us who are Christians have co-opted, and I, for one, thoroughly enjoy. So I would have to agree that, yes, the way we use it today, is as a "Christmas tree."
I believe the country was founded on a principle of freedom from government-mandated religion. Many, not all, of the people who were first here were some type of Christian denomenation. Spirituality, faith in God, etc. were all part of the early European settlers beliefs. (Although the Native Americans, who were here first, weren't Christian at that point in time.)
The point in going to a "holiday" tree or some form of what we now call "political correctness" was to acknowledge that not everyone in this country believes in some form of Christianity. I believe it was an attempt to embrace all Americans in a time of the year that almost every faith from time immemorial has acknowledged as very spiritually powerful. True, forcing the use of "holiday tree" is probably a bit overboard, but let's remember the intention.
And let's remember that for Christians, Christ's birth is a wonder and the peace and love that he brought forth on his brief time on earth is amazing.
Let's celebrate it in the lights we see on all the trees and reflected in the faces of all our fellow Americans, whatever their faith.
How important is it what we call the tree?