form closes after execution of slot

hi to all, I've centos7.5 and Qt 5.7 in VM. I am building a small project in this i shows a form in click on button of first form. On second form there is a "on_lineEditYesNo_returnPressed()" slot. this having following code :-

Code:

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void dialogBill::on_lineEditYesNo_returnPressed()
{
    QString ch;
    QString yn1 = "y";
    QString yn2 = "n";
    ch = ui->lineEditYesNo->text().toUpper().trimmed();
 
    if( (QString::compare(ch, yn1, Qt::CaseInsensitive))  == 0 )
    {
        ui->lineEditEnterMembershipNumber->setDisabled(false);
        ui->lineEditEnterCardNumber->setDisabled(false);
        ui->lineEditYesNo->setText("");
        ui->pushButtonReturnToMenu->setVisible(true);
        ui->pushButtonReturnToMenu->setEnabled(true);
    }
    else if( (QString::compare(ch, yn2, Qt::CaseInsensitive)) == 0)
    {
        ui->lineEditYesNo->setText("");
        ui->pushButtonReturnToMenu->setEnabled(false);
        parentWidget()->show();
    }
}

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problem is that after execution of this slot ( reaching at end ) this second form automatically closes. I don't want to do this.
please have any suggestion.