The chant is transcribed from these two facsimiles(1 2). The originals contain the medieval melody notation too. There's a loose connection with Mark 11 describing the final passage of Jesus from the Mount of Olives and his triumphant entry in Jerusalem.
Many thanks to the Library of Switzerland
 
In the video the chant from a concert of the Capilla del Sol ensemble and starts exactly at 9:14. You can also admire their traditional instruments