Firebase Button onClick, set UID child - firebase

Question

I have an problem with Firebase!, I've created register and login page and works fine!. but i have an problem. why my button create a new 'child'?
How can i put button 'onClick' on same UID from identify users by button clicks ? What I want to do, I don't know how firebase works 100% can anyone explain for me? i really need to {get} does click buttons for identify every user on database. My page button
MainActivity
public class MainActivity extends AppCompatActivity {
private Button influenciador;
private Button marca;
private DatabaseReference mDatabase;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
influenciador = (Button) findViewById(R.id.BotaoSouInfluenciador);
marca = (Button) findViewById(R.id.BotaoSouMarca);
mDatabase = FirebaseDatabase.getInstance().getReference().child("Usuários");
influenciador.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
mDatabase.child("Usuários").push().setValue("Pizza");
openDIContrato();
}
});
marca.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
mDatabase.child("Usuários").setValue("Burger");
openMarcaContrato();
}
});
}
public void openDIContrato() {
Intent intent = new Intent(this, DIContrato.class);
startActivity(intent);
}
public void openMarcaContrato() {
Intent intent = new Intent(this, MarcaContrato.class);
startActivity(intent);
}
}
Users class
public class Usuarios {
private String id;
private String email;
private String aniversario;
private String senha;
private String nome;
private String sexo;
public Usuarios() {
}
public void salvar(){
DatabaseReference referenciaFirebase = ConfiguracaoFirebase.getFirebase();
referenciaFirebase.child("Usuários").child(String.valueOf(getId())).setValue(this);
}
#Exclude
public Map<String, Object> toMap(){
HashMap<String, Object> hashMapUsuario = new HashMap<>();
hashMapUsuario.put("id", getId());
hashMapUsuario.put("email", getEmail());
hashMapUsuario.put("aniversario", getAniversario());
hashMapUsuario.put("nome", getnome());
hashMapUsuario.put("sexo", getSexo());
return hashMapUsuario;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public String getSenha() {
return senha;
}
public void setSenha(String senha) {
this.senha = senha;
}
public String getnome() {
return nome;
}
public void setnome(String nome) {
this.nome = nome;
}
public String getAniversario() {
return aniversario;
}
public void setAniversario(String aniversario) {
this.aniversario = aniversario;
}
public String getSexo() {
return sexo;
}
public void setSexo(String sexo) {
this.sexo = sexo;
}
}

Answer 1

You're not using the correct reference to your database. From the image with title "what I want to do", you can do so with this piece of code:
DatabaseReference ref = FirebaseDatabase.getInstance().getReference().child("Usuários");
ref.child(iD).child("Button").setValue("Pizza");
//id is the string I can see in the databse image dG9ue...