Main Menu Bar doesn't show up in OS X

[CroCo]

I've created simple QMainWindow application in mac. I've added File->new, File->save, and Help. Running the application, the menu doesn't show up. It shows the following

This is the designer form

macOS High Sierra Version 10.13.2
Qt Creator 4.3.1
Based on Qt 5.9.1 (Clang 7.0 (Apple), 64 bit)

[kenchan]

This is a Mac so the main menu is at top of the screen in the common menu. Usually it does not sit on top of of the app window.