In 1991 Stephen Stills released Stills Alone, an album that was stripped down versions of mostly new tunes. Treetop Flyer became a staple of his and CSN's concerts for the next couple decades.
The song is played in Dropped D Tuning and is really just a 4-measure progression. Of course, it is extended by Still's improvising, and he never plays it exactly the same.
This lesson breaks down the studio intro and then shows lots of the ways that Stills plays through the progression, including a look at his first interlude and thoughts on the D Minor Pentatonic scale, which is used for all the improvised sections.