<code C++>
#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QTreeWidgetItem>
#include <QDir>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

private slots:
    void on_pushButton_clicked();

private:
    Ui::MainWindow *ui;
    void showDir (QTreeWidgetItem * target, QDir dir);

};

#endif // MAINWINDOW_H

</code>

<code C++>

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
}

MainWindow::~MainWindow()
{
    delete ui;
}

#include <QDir>

void MainWindow::showDir (QTreeWidgetItem * target,
                          QDir dir)
{
    QFileInfoList list = dir.entryInfoList
            (QDir::NoDotAndDotDot | QDir::AllEntries, QDir::Name);

    for (QFileInfo info : list)
    {
        QTreeWidgetItem * node = new QTreeWidgetItem;
        node->setText (0, info.fileName());
        node->setToolTip(0, info.absoluteFilePath());
        QColor color;
        if (info.isDir())
            color = QColor ("red");
        else
            color= QColor ("blue");
        node->setForeground (0, color);
        target->addChild (node);
        if (info.isDir())
           showDir (node, QDir (info.absoluteFilePath()));
    }
}

void MainWindow::on_pushButton_clicked()
{
    QDir dir ("..");

    QTreeWidgetItem * item = new QTreeWidgetItem;
    item->setText (0, dir.absolutePath());
    item->setForeground (0, QColor ("red"));
    ui->treeWidget->addTopLevelItem (item);

    showDir (item, dir);
    item->setExpanded (true);
}

</code>