Sets iter to point to the first child of parent. If parent has no
children, FALSE is returned and iter is set to be invalid. parent
will remain a valid node after this function has been called.
If parent is NULL returns the first node, equivalent to
gtk_tree_model_get_iter_first (tree_model, iter);
Sets iter to point to the first child of parent. If parent has no children, FALSE is returned and iter is set to be invalid. parent will remain a valid node after this function has been called. If parent is NULL returns the first node, equivalent to gtk_tree_model_get_iter_first (tree_model, iter);