Yes, it's been up since before Thanksgiving
Yes, it's been up since between Thanksgiving and December 1st.
Yes, it's been up since the first week of December (i.e. between the 2nd and the 7th)
Yes I/we just put it up sometime in the last week (i.e. between the 8th and the 12th)
It's gone up (or going up) today!
No, but it will probably go up sometime between tomorrow and the 20th.
No, it's probably going up sometime between December 21st to the 23rd
No, it will go up on December 24th (Christmas eve)
No, I/we don't plan to put up a Christmas tree this year (but I have in the past)
No, I/we never put up a Christmas tree
Something else (what?)