The tune is an adaptation of the pipe jig "The Athol Highlanders", with the chorus taking part one of the tune. That's why the first three lines of the chorus begin with "Oh", and the fourth line confuses the chorus singers by not having an "Oh". In my childhood the family tradition whenever this tune was played, as march or jig, was for us to sing along:
Oh, oranges, oranges, oranges,
Oh, oranges, oranges, oranges,
Oh, oranges, oranges, oranges,
Oranges, oranges, oranges, oranges.

Oranges, oranges, oranges, oranges,
Oranges....etc
through all four parts of the tune.

Why we sang it, or how old the tradition was, I don't know, but we always ended up smiling.