g-menu-insert-submenu (menu position label submenu)

menu -- a g-menu object
position -- an integer with the position at which to insert the item
label -- a string with the section label, or nil
submenu -- a g-menu-model object with the items of the submenu

Convenience function for inserting a submenu menu item into the menu. Combine the functions g-menu-item-new-submenu and g-menu-insert-item for a more flexible alternative.