In Vol 1 of this book the aim is to move on from the pentatonic as exemplified in Kodaly's 333 Reading Exercises to the full range of heptatonality.
In Vol 2 can be found folk tunes of a wider tonal range, with accidentals etc., and more challenging rhythms.
As the pages of Kodaly's 333 alternate between stick notation and the stave, so here György Tegzes follows the same alternating pattern.