GListStore already has a g_list_store_insert_sorted function,
which can be used to keep the list sorted according to a fixed
sort function. But if the sort function changes (as e.g. with
sort columns in a list UI), the entire list needs to be
resorted. In that case, you want g_list_store_sort().

https://bugzilla.gnome.org/show_bug.cgi?id=754152