In Trees is a great piece to learn if you enjoy experiementing with open tunings. Open tunings are a big part of the acoustic guitar world. For this song she tunes her guitar DADF#AC#.
It features lots of slides and hammer ons and pull offs. Make sure you practice the piece slowly!
From a songwriting perspective a fingerstyle part like this is a great way to make an accompaniment more interesting. A part like this is much better than just strumming chords!
There is the standard YouTube Video and PDF but why not try out the interactive soundslice tab