Sub column Headers in Pivot Table

I am trying to achieve a pivot table format, where there are multiple column headers under one. I am attaching the screenshot for the format here. As the fields are text and date fields, i am not able to achieve that format directly through the pivot widget. 

I also tried out a script to format this, but there was no change on the table. Attaching the script below. 

widget.on("ready", function(w, args) {

var style = {
'font-size' : '12px'
,'font-weight' : 'bold'
,'color' : 'white'
,'background-color' : '#7a7a7a'
,'text-align' : 'center'
,'vertical-align' : 'middle'
}

//header columns
$(".p-dim-member-head", element).css(style);
$(".p-measure-head", element).css(style);

});

 

Could someone please help me achieve this pivot format. 

Thanks
Hema