setvisible() of QWidget has no effect at QTreeWidgetItem

pbtn->setVisible(false);

#include <QMainWindow>

#include <QTreeWidget>
#include <QTreeWidgetItem>
#include <QPushButton>


namespace Ui {
    class MainWindow;
}

class MainWindow : public QMainWindow {
    Q_OBJECT
public:
    MainWindow(QWidget *parent = 0);
    ~MainWindow();

protected:
		void changeEvent(QEvent *e);

private:
    Ui::MainWindow *ui;

	private slots:
		void click123();
};

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


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

		QTreeWidgetItem *widget_item;

		widget_item = new QTreeWidgetItem();
		widget_item->setText(0, "example text");

		QPushButton *pbtn;

		pbtn = new QPushButton();
		pbtn->setText("example");
		pbtn->setVisible(false);

		ui->treeWidget->addTopLevelItem(widget_item);

		ui->treeWidget->setItemWidget(widget_item, 0, pbtn);

}

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

void MainWindow::changeEvent(QEvent *e)
{
    QMainWindow::changeEvent(e);
    switch (e->type()) {
    case QEvent::LanguageChange:
        ui->retranslateUi(this);
        break;
    default:
        break;
    }
}

void MainWindow::click123() {


}