甘特图，隐藏列实现echarts 柱状配置项内容和展示

如何让绿色部分透明，只留下红色部分，得到甘特图,像截图那样

      option = {
    title: {text: '甘特图'},
    name: '如何让绿色部分隐藏，只留下红色部分',
    tooltip: {},
    dataset: {
        sourceHeader:false,
        dimensions: ['product', {name:'start', type:'time'}, {name:'end', type:'time'}],
    // 提供一份数据。
        source: [
            ['任务一', '2017-05-10', '2017-05-11'],
            ['任务二', '2017-05-12', '2017-05-14'],
            ['任务三', '2017-05-15', '2017-05-17'],
            ['任务四', '2017-05-19', '2017-05-20']
        ]
    },
    yAxis: {type: 'category'},
    xAxis: {
        type:'time',
        min: '2017-05-01'
    },
    series: [
        {
            type:'bar',
         	stack:  '计划',  
            encode: {
                y: 'product',
                x: 'end',
            },
            label: {
                normal: {
                    show: true,
                    position: 'inside'
                }
            },
        },
        {
	        type:'bar',
	     	stack:  '计划',
     	    name: '辅助',
	        data: [
				'2017-05-10',
				'2017-05-12',
				'2017-05-15',
				'2017-05-19',
			],
            itemStyle: {
                normal: {
                    barBorderColor: 'rgba(0,0,0,0)',
                    color: 'green'
                },
                emphasis: {
                    barBorderColor: 'rgba(0,0,0,0)',
                    color: 'green'
                }
            },
    	}
    	]
};