These chords are not used in the song but they are suggested by the melody if you 
to play the song on guitar these are the chords I would use

         D
Well the hills are pretty and rollin'
        C
But the thorn is sharp and swollen
        D
And the man plays a beautiful whistle
       C
But he wears a prickly thistle
        D
Singing Li De Li De Li Oh Oh
     C
Well A Li De Li De Li Oh Oh
D
Li De Li De Li Oh Oh
     C
Well A Li De Li De Li Oh Oh

    D
The silver birches pierce through an icy fog
      C
Which covers the ground most daily
        D
And the angels which carry St. Andrew high
    C
Are singing a tune most gaily

    D
One sound can hold back a thousand hands
     C
When the pipe plays a tune forlorn
     D
And the thistle is a prickly flower
     C
Aye, But how it is sweetly worn
        D
Singing Li De Li De Li Oh Oh
     C
Well A Li De Li De Li Oh Oh
D
Li De Li De Li Oh Oh
     C
Well A Li De Li De Li Oh Oh