first try to create a config tree build

StorageBundle/DependencyInjection/Configuration.php

@@ -16,7 +16,17 @@ class Configuration implements ConfigurationInterface
     public function getConfigTreeBuilder()
     {
         $treeBuilder = new TreeBuilder();
-        $treeBuilder->root('storage');
+        $root = $treeBuilder->root('storage');
+        $root->children()
+            ->arrayNode('storage_name')
+                ->children()
+                    ->scalarNode('type')->end()
+                ->children()
+                    ->scalarNode('bucket')->end()
+                ->children()
+                    ->scalarNode('region')->end()
+                ->children()
+                    ->scalarNode('endpoint')->end();
         return ($treeBuilder);
     }
 }

StorageBundle/Storage.php

@@ -26,7 +26,7 @@ class Storage
 
 //storage:
 //photos:
-//type: s3
+//      type: s3
 //      bucket: bluesquare.public
 //      region: nl-ams
 //      endpoint: 'https://s3.nl-ams.scw.cloud'