Take your old Christmas tree out to the compost pile rather than the curb, limb it up, and then find a place to set the trunk aside to finish drying — wood tends towards having knots, but is relatively straight.
If you’re in a lyrical / poetic mode, you could make ornaments / gifts out of it for next year, ideally incorporating an image of the tree.
(Shades of the religious folk story about the three trees for folks who are Christian)