So asside from pilot and trainee
Did anyone else see the drone? also if a helicopter is so close to the ground that they were unable to avoid hitting a tree then was the drone actually doing anything wrong? Who is most responsible for a crash when the drone doesnt actually hit anything.
If the crap pilots could get away with "the tree jumped into my aircraft " then you could bet that there would be calls for legislation to remove trees. So I would say that drone claims need to be backed up with indepedant witnesses
To this end I would say human carrying aircraft need dash cameras, I am not saying that there are no drone pilots who are dicks merely that currently "a drone made me do it" seems a very popular excuse for crashes.
Lastly I do not have a drone but it would seem that the simpless answer is to not allow drones to fly outside of drone approved airspace and passenger aircraft not to fly in drone space, a simple height limiter for both and a signal strength limit on RC transmitter would seem to be sufficent. If the drone is flying beyond your range of vision then can it be said to be under control and once it looses signal it should autoland. Similarly private helicopters flying at tree height outside of designated areas surrounded by a no drone area should not be allowed. Personally I would question the sanity of any occasion where any aircraft needed to land or fly outside of an designated area.