Chromatic button accordions, familiarly known as CBAs, have buttons on both bass and treble sides. Like piano accordions, they play the same note on the push and pull of the bellows, and they typically have a Stradella bass (see piano accordions).
A CBA with at least five rows of treble buttons has the same scale pattern in any key. Many have buttons that are color-coded to correspond to the white and the black keys of a piano.
Some buttons are duplicates, so a treble keyboard has more buttons than notes. On the plus side, that gives you options for where to play a particular note, so you don’t necessarily have to move your fingers very far to get them where you them want to be.
There are several standard layouts for the treble side. Most common in Italy and on the streets of Paris is the C-system; in Russia and in Scandinavia, any one of several B-systems, which are more or less the mirror image of the C-system. One isn’t necessarily better or easier than the other; just different. They are versatile and powerful instruments, but learning aids are scarce, especially in English.