This guy Jesse on Alone Season 5 was running out of food and had read about native tribes creating bread from tree bark, so he stripped some off a pine tree and ate it. It seemed edible but hard to pass. The video shows the aftermath, basically he had to tap out and be rescued due to severe abdominal pain. However, apparently it is a thing, I’m not sure how you could do it in a way your stomach can handle though, and most likely it has to be specific species of trees.