Calling it a "shame" that people throw out Christmas tree "as if they were garbage," chef René Redzepi (of the restaurant Noma in Copenhagen) would like you to cook and eat it. It's like hyper-local foraging, except you're foraging in your living room. In an op-ed for the New York Times, Redzepi writes: "Nature takes enormous time and effort to produce something that we use only briefly. Why don’t we make greater use of this living tree, as we make use of so many other kinds of plants on earth, by eating it?"
Announcing that "evergreens are delicious," he goes on to list a whole bunch of uses: One can dry and mix the needles "into a powder that makes a light, citrus-y and very aromatic spice." Said powder could then be sprinkled onto cookie dough, added to rice, or rubbed onto a chicken. Or cooking with small spruce or fir branches "as you would a sprig of rosemary or thyme" — he suggests fish, infused oils, steamed spinach, steak, and game meats.
Redzepi continued: "I don’t mean to sermonize. I want only to point out that food is everywhere, that a tree is more than a symbol or a decoration: it is delicious food." He also provides recipes, including one for spruce butter.
Commenters did bring up a valid point, however: that one should be aware of the provenance of a tree, for some have been treated with pesticides, fire-retardant chemicals, or even pine odor. Sometimes trees even have kittens in them. So do be careful!