--- /dev/null
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Config\Definition\Builder;
+
+use Symfony\Component\Config\Definition\NodeInterface;
+
+/**
+ * This is the entry class for building a config tree.
+ *
+ * @author Johannes M. Schmitt <schmittjoh@gmail.com>
+ */
+class TreeBuilder implements NodeParentInterface
+{
+ protected $tree;
+ protected $root;
+ protected $builder;
+
+ /**
+ * Creates the root node.
+ *
+ * @param string $name The name of the root node
+ * @param string $type The type of the root node
+ * @param NodeBuilder $builder A custom node builder instance
+ *
+ * @return ArrayNodeDefinition|NodeDefinition The root node (as an ArrayNodeDefinition when the type is 'array')
+ *
+ * @throws \RuntimeException When the node type is not supported
+ */
+ public function root($name, $type = 'array', NodeBuilder $builder = null)
+ {
+ $builder = $builder ?: new NodeBuilder();
+
+ return $this->root = $builder->node($name, $type)->setParent($this);
+ }
+
+ /**
+ * Builds the tree.
+ *
+ * @return NodeInterface
+ *
+ * @throws \RuntimeException
+ */
+ public function buildTree()
+ {
+ if (null === $this->root) {
+ throw new \RuntimeException('The configuration tree has no root node.');
+ }
+ if (null !== $this->tree) {
+ return $this->tree;
+ }
+
+ return $this->tree = $this->root->getNode(true);
+ }
+}