// main.cpp
#include <QtGui/QApplication>
#include <QtGui/QTreeWidgetItem>
#include <QtGui/QMessageBox>
#include "subitem.h"

int main(int argc, char *argv[]) {
   QApplication app(argc, argv);

   QTreeWidget *tree = new QTreeWidget();
   tree->show();

   SubItem *item = new SubItem(tree);
   item->setText(0, "Item");

   SubItem *item2;
   item2 = static_cast<SubItem *>(tree->topLevelItem(0));

   return app.exec();
}

// subitem.cpp
#include "subitem.h"

SubItem::SubItem(QTreeWidget* parent) : QTreeWidgetItem(parent) {
};

// subitem.h
#ifndef SUBITEM_H
#define SUBITEM_H

#include <QTreeWidgetItem>

class SubItem : public QTreeWidgetItem {
   Q_OBJECT
   public:
      SubItem(QTreeWidget* parent);
};
#endif // SUBITEM_H

TARGET = Tst
TEMPLATE = app
SOURCES += main.cpp \
    subitem.cpp
HEADERS += subitem.h