function insert_term( $name,$tax,$parent='' ,$slug='') {
    $term_id = term_exists( $name, $tax);
    if ( !$term_id)
        $term_id = wp_insert_term( $name, $tax, array('parent'=>$parent,'slug'=>$ludg) );
    return $term_id;
}

insert_term('USSERS','category');