How to iterate in FirebaseDatabase randomly

I have an adapter that shows the users that are passed to a list, testData is the List variable

adapter = new SwipeDeckAdapter(testData, getContext());
    if (cardStack != null) {
        cardStack.setAdapter(adapter);
    }

i add the data from FirebaseDatabase and i try to Iterate Randomly but just pass the first value of the Database, this is my structure

 "ListaTrabajadores" : {
"TrabajadoresH" : {
  "Ecuador" : {
    "Quito" : {
      "6fvnKNboraZNIecImpAFtrtdwZA3" : {
        "id" : "6fvnKNboraZNIecImpAFtrtdwZA3"
      },
      "8nhcInO7A2eODlz8MS3LuMwXONj2" : {
        "id" : "8nhcInO7A2eODlz8MS3LuMwXONj2"
      },
      "DOPPWREd1uZoYRQr5wdbiUz8d4N2" : {
        "id" : "DOPPWREd1uZoYRQr5wdbiUz8d4N2"
      }
    }
  }
}
}

my code just shows the First Id and just shows the first User this is the first ID

"6fvnKNboraZNIecImpAFtrtdwZA3" : {
    "id" : "6fvnKNboraZNIecImpAFtrtdwZA3"

this is my code to iterate over firebase and add the data in the List

private void getDataMale() {

    if (ciudadX != null && paisX != null) {
        FirebaseUtils.getMeetPeopleListCitySexoMasculinoReference(paisX, ciudadX).addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                if (dataSnapshot != null && dataSnapshot.getChildrenCount() >= 1) {



                    for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
                            MeetList ml = snapshot.getValue(MeetList.class);
                                if (ml.getID().equals(firebaseUser.getUid())) {
                                    // nothing, are you
                                }else{
                                    testData.add(ml);
                                    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1) {
                                        if (!getActivity().isDestroyed()) {
                                            adapter.notifyDataSetChanged();
                                        }else if (Build.VERSION.SDK_INT <= Build.VERSION_CODES.JELLY_BEAN_MR1) {
                                            // nada
                                        }
                                        return;

                                    }
                                }



                    }
                }else if (dataSnapshot.getChildrenCount() == 0) {
                    mLinearAvisoVacio.setVisibility(View.VISIBLE);
                    mTextViewAviso.setText("Por el momento no hemos encontrado a nadie en tu ciudad, vuelve mas tarde");

                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });
    } else {
        mTextViewAviso.setText("No hemos podido encontrar tu ciudad, activa el gps o intentalo mas tarde");
        AlertDialog alertDialog = new AlertDialog.Builder(getContext(), R.style.Theme_AppCompat_Light_Dialog).create();
        alertDialog.setTitle("No podemos encontrar tu ciudad, intentalo mas tarde");
        alertDialog.setCanceledOnTouchOutside(false);
        alertDialog.setButton(AlertDialog.BUTTON_POSITIVE, "Ok ", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(final DialogInterface dialog, int which) {
                dialog.dismiss();
                mLinearAvisoVacio.setVisibility(View.VISIBLE);

            }
        });

        alertDialog.show();
    }


}

I need to iterate Randomly to add to the list and in the list Shows the user randomly