It's the Christmas tree, stupid.
I don't mean you're stupid. I just mean the question is a little daft.
For as long as I can remember, I have loved Christmas trees. When I was small, we still got real trees (my mom and I are deathly allergic, so now we all have fake trees), and the process would begin by the family heading out to a Christmas tree lot to pick out a tree. My sisters and I didn't really care about the tree, per se. We were more interested in running around through the maze of trees, playing hide and seek. Usually the tree choosing evening also included a meal at someplace like McDonald's, which was a treat for us.
But the real magic began when my mom pulled out the ornaments so we could start trimming the tree. All those lovely treasures that we hadn't seen for a year -- it was such fun to go through them and find the ones we'd missed the most. For me, it was the ceramic faeries, one for each of us (my mom tried to get rid of them a few years ago, but I rescued them and now they hang on our tree).
The lights are the most important part for me. I love the lights. The lights are the entire point. The Christmas tree is a holdover from pagan traditions to welcome the Winter Solstice. Lights were placed in trees to ward off evil spirits. In this day and age, I only know of one evil spirit that I need to ward off: the dark and cold that characterize this time of year. So I love to sit with the tree lights on and drink tea and read a book and listen to George Winston's December album. It fills me with peace.
Also, my Grandma McEwen loved Christmas trees. She used to try to teach me how to sing "O Tannenbaum" in German. I never quite grasped it, but she never stopped trying. Anything Grandma McEwen loved, I was willing to love.
The Christmas tree makes Christmas. As soon as it's up, it becomes the Christmas season.