My mam used to sing me the song "Billy Boy" when I was a wee girl. So, it’s a song tune, but it makes a great lively whistle tune too.
There’s a version of it which is a little bit different here: http://www.gutenberg.org/files/20774/20774-h/20774-h.htm#Billy_Boy
so the tune is not about condomes 😉 ?
Oh how innocent I was!