A melody heard on the railway train

No idea whose melody it is, or if the young woman playing had been improvising on the accordion. There was a man and a baby with her.


The melody was ascending step by step starting from A but ending to sustained B one octave above. A register of parallel double octaves or something must had been set on the accordion. The girl was looping this rather interesting melody:


A        B
C D E F
G A B
    A G A
G F G F
E F E D
C D
.   .   .   .
.   .   .
goto begining