Actually - we OWN a x-mas tree farm, so Morgan has been around xmas trees since she was 2 months old.
She was born Oct. 5 of last year so she is 7 months old.
We did have a real tree (obviously! - Although by the time we're done selling I usually say "forget the tree this year!" But always end up putting one up!)
We actaully did not put any ornaments on the bottom of the tree - OR lights. You don't want your baby biting on the lights - and being an electrician, my husband reminded me of that!
Also make sure that the plugs are WAY inaccessible to your baby.
I would recommend a gate especially if you do not crate your dog when you leave.
Our furbaby is crated when we are gone - not only for her safety, but for my sanity!
I think that if you take the necessary precautions, it shouldn't be a problem.
But - definitely make sure that she is not allergic ahead of time.
Maybe go to a local farm and ask to cut off a branch on the bottom for her to sniff to see if there's a reaction.
And don't forget to keep that tree watered continuously and don't let it ever run out! A non-watered tree is a major fire hazard!
Happy early xmas
