I'm in trouble to display a picture in QMainWindow using QLabel. I even copied the code from tutorial, but the compiler still fails to compile it. It always remind me a QLabel member is not defined.

Here's my code :
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Error Information:
Ui::WindowClass has no member "imageLabel"
---------------------------------------------------------------------
/*Window.h*/
#include <QtWidgets/QMainWindow>
#include <QtWidgets/QLabel>
#include "ui_window.h"

class Window : public QMainWindow {
Q_OBJECT
public:
Window(QWidget *parent = 0) {}
private:
Ui::WindowClass *ui;
QLabel *imageLabel;
};
---------------------------------------------------------------
/*Window.cpp*/
#include "window.h"
#include "ui_window.h"

Window::Window(QWidget *parent) : QMainWindow(parent), ui(new Ui::WindowClass) {
ui->setupUi(this);
QImage image("./Resources/Tree.png");
ui->imageLabel->setPixmap(QPixmap::fromImage(image));
}
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I know the imageLabel member is declared in Window, not in Ui::WindowClass, but how can I fix it?
BTW, I use Qt5 and VS2013