Adding menus to SECOND submenu - no go

OpenGL OpenGL: Basic Coding
1 
I understand OpenGL has limited build-in (pop-up) menu functions, but this got  me stumped.

Am I limited to one submenu?

   // submenu
submenu_id = glutCreateMenu(OpenGL_menu); // callback (?)
glutAddMenuEntry("Sphere", 2);
glutAddMenuEntry("Cone", 3);
glutAddMenuEntry("Torus", 4);
glutAddMenuEntry("Teapot", 5);

// sucessfuly added
glutAddMenuEntry("Unity viewport ", 6);
glutAddMenuEntry("Unity circle ", 7);
// second submenu successfully created
submenu_Smith = glutCreateMenu(OpenGL_menu); // callback (?)
// cannot add to second submenu
glutAddMenuEntry("Unity viewport ", 2);
glutAddMenuEntry("Unity circle ", 3);

menu_id = glutCreateMenu(OpenGL_menu); // main menu 
glutAddMenuEntry("Clear", 1);
glutAddSubMenu("Draw", submenu_id);
glutAddMenuEntry("Quit", 0);

// successfully added
glutAddMenuEntry("Smith chart submenu ", submenu_Smith);
glutAttachMenu(GLUT_RIGHT_BUTTON);

2

I understand OpenGL has limited build-in (pop-up) menu functions

OpenGL does not have menu functionality, pop-up or otherwise. GLUT does, but OpenGL itself does not. Don’t confuse the two.

3

Would it be asking too much not to nit-pic on terminology / spelling etc and help me to solve the issue?

Thunder is good, thunder is impressive; but it is lightning that does the work.

Mark Twain

4

No.

This should be glutAddSubMenu, not glutAddMenuEntry.

5

Mea culpa
Thank you very much