The immediate clues to me were...

'I have been lying on yonder bull-rushes,
Which lies beneath yond tree.'

and especially...

'Because he killed two pretty little birds,
Which flew from tree to tree.'

Both found in Edward, it was clear to me when I first saw it. Also this establishes a Version I whether misplaced or not. Version E is not from Motherwell p. 60, it's a collation and is found on p. 270 of the Ballad Minstrelsy of Scotland. Maybe I missed something,

Richie