protected function _addTree(Zend_Server_Reflection_Node $parent, $level = 0)
    {
        if ($level >= $this->_sigParamsDepth) {
            return;
        }

        foreach ($this->_sigParams[$level] as $value) {
            $node = new Zend_Server_Reflection_Node($value, $parent);
            if ((null !== $value) && ($this->_sigParamsDepth > $level + 1)) {
                $this->_addTree($node, $level + 1);
            }
        }
    }