gio:menu-insert-section (menu pos label section)

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

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