This earlier discussion contains a couple of variants and links to all the ones I could find in the Digital Tradition database and in the Forum, together with a few elsewhere:  Lyr/Chords Req: The Nightengale Sings

The best-known "Pretty Betty" version is probably that found by Sabine Baring Gould in a number of parts of Cornwall at the end of the 19th. century; the tune, which he originally got from a Mr. E.F. Stevens of St. Ives, was widely popularised through school songbooks, though there is little trace of the sexual subtext which informs most traditional versions.  We sang it at school in the early 1960s, pretty much to the words given by James Henry Dixon in  Ancient Poems, Ballads, and Songs of the Peasantry of England  (1846); I expect it still happens.  See, amongst other places:

The Nightingale  (with sound samples).

It's sometimes sung in Cornish, too, (An Eos Whek), though that's a modern translation into Cornish, made as part of the Cornish Revival movement.

See also  The Traditional Ballad Index:

One Morning in May (To Hear the Nightingale Sing) [Laws P14]

Malcolm