QSqlquery query;
query.prepare("select DeviceName from Devices" );

if(query.exec())
{
ui->treeWidget_Device->setColumnCount(1);

QList<QTreeWidgetItem *> items;

for (int i = 0; i < 10; ++i) // here I have confusion about list numbers. my
//list is verx big and will be added more

item.append(new QTreeWidgetItem((QTreeWidget*)0, QString("item:%1").arg(i)));   //this is an example with simple string but
                           //  I want to show my query in here
ui->treeWidget_Device->insertTopLevelItems(0, items);

}