This arrangement pairs the traditional text with an Irish folk tune. This tune is called “The Meeting of the Waters”, and has nothing whatsoever to do with Christmas. However, it fits the traditional Christmas text very nicely, having a very lullabyish feel to it, if I may be allowed to coin a term of highly limited usefulness. This is accompanied by organ and obbligato soprano instrument - either flute or oboe would work, as, I suppose, would a violin.
A performance of this arrangement may be heard on The Pittsburgh Camerata's album "A Pittsburgh Wassail." It is available on iTunes.