Insert additional data in Firebase

I'm developing an app that is composed of 3 Fragments of register, here given the example of A, B, C, where B and C is dependent on A.

What is the best way to enter data that is populated in B and C in the same Child of Fragment A within Firebase.

I used Fragment A:

.child("Profissional").child(idUsuario).child("A").push().setValue(this);

and in B and C:

firebase.child("Profissional").child(idUsuario).child("A");

While saving save data I saved Fragment A.