code: public function getConfigTreeBuilder()
      {
          $treeBuilder = new TreeBuilder();
          $rootNode = $treeBuilder->root($this->root);
  
          $resourceDefinition = $rootNode
              ->children()
              ->arrayNode('configurations')
              ->useAttributeAsKey('code')
              ->prototype('array')
              ->performNoDeepMerging()
              ->children();
  
          $this->appendResourceDefinition($resourceDefinition);
  
          $resourceDefinition->end()
              ->end()
              ->end()
              ->end();
  
          return $treeBuilder;
      }
docs: {@inheritdoc}
  @throws \RuntimeException