Once upon a time, I put off getting a tree until it was too late, not one was to be found in shop or on market stall. This was before artificial trees were anything like realistic, so being me, I decided that if I must have a fake tree, I'd jolly well have a stylized one with no pretensions to authenticity.
A bedsheet-sized piece of black cloth was bought, hemmed to fit over a broomstick as a hanger, and hung on the wall. On it I pinned thick green tinsel forming the outline of a tree, a dozen lights, a few baubles and some thin tinsel. It looked perfect, it took up no space and the cats didn't bother it. I re-used it for several years until eventually I needed the black material for another purpose. Now, I don't bother with a tree at all, even a 2-dimensional one, I just hang lights in the windows with greenery and decorations on the picture rail.

To answer the date question, for me it's December 17th. Always 17th. The official Christmas season lasts for 12 days, so I allow 11 for my own birthday on St. Nicholas' Day before the cards and decorations go up.