在Highcharts中，如何为多金字塔图表中的每个金字塔设置标题

<script src="https://code.highcharts.com/highcharts.js"></script>

<div id="container"></div>

Highcharts.chart('container', {
    chart: {
        type: 'pyramid'
    },
    title: {
        text: '多金字塔图表'
    },
    series: [{
        name: '金字塔1',
        data: [
            ['A', 100],
            ['B', 80],
            ['C', 60],
            ['D', 40],
            ['E', 20]
        ]
    }, {
        name: '金字塔2',
        data: [
            ['X', 120],
            ['Y', 90],
            ['Z', 70]
        ]
    }],
    plotOptions: {
        series: {
            dataLabels: {
                enabled: true,
                format: '<b>{point.name}</b> ({point.y})'
            },
            center: ['50%', '50%'],
            width: '60%'
        }
    }
});