How to allow colspan and rowspan for export excel in datatable jquery plugin

Question

<table>
    <thead>
        <tr>
            <th colspan="4" align="center">This is header</th>
        </tr>
        <tr>
            <th>S.No</th>
            <th>Class Name</th>
            <th>Section</th>
            <th>Enrollment Code</th>
        </tr>
    </thead>
    <tbody>
        <tr>
            <td>1</td>
            <td>1st</td>
            <td>A</td>
            <td>101</td>
        </tr>
        <tr>
            <td>1</td>
            <td>1st</td>
            <td>A</td>
            <td>101</td>
        </tr>
    </tbody>
</table>

The above is my table with header colspan and rowspan, for the table i am adding data table plugin as below

$('table').DataTable({
            "scrollX": true,
            "paging": true,
            "bSort": false,
            "sScrollXInner": "100%",
            "lengthMenu": [[50, 100, 500, -1], ["50", "100", "500", "All"]],
            dom: 'Bfrtip',
            buttons: [
                'excelHtml5',
            ]
        });

while i am click on the export button it remove the first row and export remaining data how to allow the colspan and rowspan in export excel in datatable plugin. please help me.