Though strongly pentatonic in character, the song is cast in the diatonic scale of F major.
"The Tinguian" by Fay-Cooper Cole
We used to think for instance that in music the ordinary diatonic major scale, with its variant minor, was a fact of nature.
"A Librarian's Open Shelf" by Arthur E. Bostwick
To associate this scale with the ordinary diatonic scale let a major 9th be taken, e.g.
"Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 10" by Various