gboolean iter_parent ( GtkTreeModel* tree_model, GtkTreeIter* iter, GtkTreeIter* child )
iter to be the parent of
child is at the toplevel, and doesn’t have a parent, then
iter is set to an invalid iterator and
FALSE is returned.
child will remain a valid node after this function has been called.
iter will be initialized before the lookup is performed, so
iter cannot point to the same memory location.