sibling. If sibling is NULL, then the row will
be appended to the end of the list. iter will be changed to point to this
new row. The row will be empty after this function is called. To fill in
values, you need to call gtkListStoreSet or gtkListStoreSetValue.gtkListStoreInsertBefore(object, sibling)objectsiblingGtkTreeIter, or NULL. [ allow-none ]iterGtkTreeIter to set to the new row