My wife sings it in G and to my ears it goes -

[Daug]As [G]I passed by a willow [D]tree, willow tree
That [D7]willow leaf blew down on [G]me
I picked it [G7]up
It would not [C]break [C#dim]
I [D]passed my [D7]love he would not [G]speak [Daug]

Repeats same for all

Daugmented is probably optional but I quite like it