LI tree
     *     nodeDecorator: Closure (null) - uses $node as argument and returns decorated item as string
     *     rootOpen: string || Closure ('
') - branch start, closure will be given $children as a parameter
     *     rootClose: string ('
') - branch close
     *     childStart: string || Closure ('') - start of node, closure will be given $node as a parameter
     *     childClose: string ('') - close of node
     *     childSort: array || keys allowed: field: field to sort on, dir: direction. 'asc' or 'desc'
     * @param boolean $includeNode - Include node on results?
     *
     * @return array|string
     */
    public function childrenHierarchy($node = null, $direct = false, array $options = array(), $includeNode = false);
    /**
     * Retrieves the nested array or the decorated output.
     *
     * Uses options to handle decorations
     * NOTE: nodes should be fetched and hydrated as array
     *
     * @throws \Gedmo\Exception\InvalidArgumentException
     * @param array $nodes - list o nodes to build tree
     * @param array $options :
     *     decorate: boolean (false) - retrieves tree as UL->LI tree
     *     nodeDecorator: Closure (null) - uses $node as argument and returns decorated item as string
     *     rootOpen: string || Closure ('') - branch start, closure will be given $children as a parameter
     *     rootClose: string ('
') - branch close
     *     childStart: string || Closure ('') - start of node, closure will be given $node as a parameter
     *     childClose: string ('') - close of node
     *
     * @return array|string
     */
    public function buildTree(array $nodes, array $options = array());
    /**
     * Process nodes and produce an array with the
     * structure of the tree
     *
     * @param array - Array of nodes
     *
     * @return array - Array with tree structure
     */
    public function buildTreeArray(array $nodes);
    /**
     * Sets the current children index.
     *
     * @param string $childrenIndex
     */
    public function setChildrenIndex($childrenIndex);
    /**
     * Gets the current children index.
     *
     * @return string
     */
    public function getChildrenIndex();
}