We put our tree up in the last few days before Christmas - good sales, if you can find a tree worth using - and leave it up for the 12 days. I usually can't stand chasing the baby out of it for that long, though!
I refused, point blank, to have a Christmas tree until child # 3 was 18 months. I did not have time to protect the virtue of a *bleeping* tree! My in-laws thought I was spitting on Santa Clause.....