A radio menu item is a check menu item that belongs to a group. At each instant exactly one of the radio menu items from a group is selected.

The group list does not need to be freed, as each #GtkRadioMenuItem will remove itself and its list item when it is destroyed.

The correct way to create a group of radio menu items is approximatively this:

How to create a group of radio menu items.

GSList *group = NULL;
GtkWidget *item;
gint i;

for (i = 0; i < 5; i++)
{
  item = gtk_radio_menu_item_new_with_label (group, "This is an example");
  group = gtk_radio_menu_item_get_group (GTK_RADIO_MENU_ITEM (item));
  if (i == 1)
    gtk_check_menu_item_set_active (GTK_CHECK_MENU_ITEM (item), TRUE);
}

CSS nodes

menuitem
├── radio.left
╰── <child>

GtkRadioMenuItem has a main CSS node with name menuitem, and a subnode with name radio, which gets the .left or .right style class.