How do I add username to user when using Firebase android?

I currently started using Firebase for my Android application and I used the samples on their GitHub to create the login and register activity.

https://github.com/firebase/quickstart-android

The only thing is that I noticed that their version only has an email and password for both login and registration. I would like to add a username field at the time of registration for my users. I did find some other links that might provide an answer but I know that Firebase was recently changed and those answers didn't show the same method of registration as the example so I figured it might be different. This is my createAccount code block:

public void createAccount(String email, String password) {
    if (!validateForm()) {
        return;
    }

    showProgressDialog();

    mAuth.createUserWithEmailAndPassword(email, password).addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
        @Override
        public void onComplete(@NonNull Task<AuthResult> task) {
            if (!task.isSuccessful()) {
                Toast.makeText(LoginActivity.this, "An error occurred", Toast.LENGTH_SHORT).show();
            }
            hideProgressDialog();
        }
    )};
}