public function highstock(array $chart, bool $include_volume = false)
    {
        $array = [];
        foreach ($chart as $timestamp => $obj) {
            $line = [
                $timestamp,
                floatval($obj['open']),
                floatval($obj['high']),
                floatval($obj['low']),
                floatval($obj['close']),
            ];
            if ($include_volume) {
                $line[] = floatval($obj['volume']);
            }

            $array[] = $line;
        }
        return $array;
    }