We didn't used to put the tree up so early but in 2010 DS2 was due on the 23rd Dec so we put it up on the 8th as DH was off work and he arrived on the 9th so it was just as well!
I also have a December birthday and have very fond memories of having the tree and all the decorations up, I really want the same for DS2 but last year the tree looked tired by Christmas day and like a twig by the twelfth night!
I cut it, soak it and water it with lemonade like my Dad used to but it just doesn't work.