[Source Code]-Highchart IRREGULAR Spline with drilldown - cannot get drilldown functional-Highcharts

The issue is now that you are providing a drilldown.id on the series. You need to do it per point. For example:

 series: [{
            name: 'Things',
            colorByPoint: true,
            data: [{
                name: 'Animals',
                y: 5,
                drilldown: 'animals'
            }, {
                name: 'Fruits',
                y: 2,
                drilldown: 'fruits'
            }, {
                name: 'Cars',
                y: 4,
                drilldown: 'cars'
            }]
        }],

It looks to me like you want to have any drilldown on a point in "Fruits" to link to the same drilldown series. This is doable:

series: [{
    name: 'Fruits',
    data: [{
        x: Date.UTC(2014, 7, 19),
        y: 12,
        drilldown: 'fruits'
    }, {
        x: Date.UTC(2014, 8, 19),
        y: 5,
        drilldown: 'fruits'
    }, {
        x: Date.UTC(2014, 9, 19),
        y: 18,
        drilldown: 'fruits'
    }]
},

See update fiddle.

But here also U dont get 2 splines after clicking on fruits, u just get one. Is there any way to get that as i have the same issue fiddle https://jsfiddle.net/surya_swami/zx9dy3uj/40/

drilldown: {  series: [{id:"z1",name: "Region-1",
                     data: [{ name : "July",y: 10},
                            { name : "Aug",y: 21},
                            { name : "Sept",y: 15}]
                     },
                     {id:"z1",name: "Region-2",
                      data: [{ name : "July",y: 12},
                             { name : "Aug",y: 9},
                             { name : "Sept",y: 25}]
                     },
                     { id:'z2',name:'Region-3',
                       data : [{name:'July',y:23},
                               {name:'Aug',y:41},
                               {name:'Sept',y:31}]
                     },
                     { id:'z2',name:'Region-4',
                       data : [{name:'July',y:33},
                               {name:'Aug',y:23},
                               {name:'Sept',y:12}]
                     },
                     { id:'z2',name:'Region-5',
                       data : [{name:'July',y:31},
                               {name:'Aug',y:39},
                               {name:'Sept',y:19}]
                     }
                    ]
        }