Prior to becoming head coach of the Eagles, Nick Sirianni worked primarily as an assistant under Frank Reich, Mike McCoy and Todd Haley.
It's probably not accurate to say the Eagles' coach came from any of these “trees” – at least not how the phrase is usually deployed – but Sirianni surely learned a lot from spending years as an assistant under them.
Sirianni's first NFL job was as an offensive quality control coach for the Chiefs under Haley, from 2009-2011. After Haley was fired, Sirianni moved up to wide receivers coach under new head man Romeo Crennel.'
Sirianni moved on to work as an offensive assistant under the Chargers from 2013-17, where he mainly worked with head coach McCoy.