private function addChainNode()
    {
        $builder = new TreeBuilder('chain');
        $node    = $this->getRootNode($builder, 'chain');

        $node
            ->fixXmlConfig('provider')
            ->children()
                ->arrayNode('providers')
                    ->prototype('scalar')->end()
                ->end()
            ->end()
        ;

        return $node;
    }