The tree library functioned as a reading room. It was situated inside the carved-out trunk of the Jedi Tree found on Ahch-To's Temple Island. During Jedi Master Luke Skywalker's time of exile there, the original sacred texts of the Jedi faith were kept on a bookshelf within the library. These texts were gathered together by Skywalker himself.
Rey came across the library while trying to convince Skywalker to end his exile and assist the Resistance. Inside the chamber, the Jedi Master questioned her reasons for being on the island. Later, before departing Ahch-To for the Crait system, she took the books from the library and stored them aboard the Millennium Falcon. Shortly after this, Skywalker tried to burn the uneti tree, but the Force spirit of Yoda intervened, summoning a lightning strike that ignited the tree.
Near the summit of Temple Island, in the northern areas of the waterworld planet Ahch-To located within the Unknown Regions, was the reading room inside the hollowed-out trunk of the uneti tree. The chamber's walls were adorned with intricately designed strips of bark. A solitary stone shelf, holding the ancient texts, served as the chamber's focal point, framed by a sunburst pattern created from bark.
The design of the tree library was intended to resemble the shape of the Rebel Alliance starbird. In the early stages of film development, the Jedi library was initially conceived as a conventional building, but the idea of using a tree was eventually chosen.