<table id="exportable">
<thead>
    <tr>
        <th>Column1</th>
        <th>Column2</th>
        <th>Column3</th>
        <th>Column4</th>
        <th>Column5</th>
        <th>Column6</th>
    </tr>
</thead>
<tbody>
    <tr>
        <td>Value1</td>
        <td>Value2</td>
        <td>Value3</td>
        <td>Value4</td>
        <td>Value5</td>
        <td>Value6</td>
    </tr>
</tbody>

function exportData() {
        alasql("SELECT * INTO XLSX('UsecaseReport.xlsx',{headers:true})
        FROM HTML('#exportable',{headers:true})");
    };

<table id="exportable">
<thead>
    <tr>
        <th colspan="2"></th>
        <th colspan="2">Group Header</th>
        <th colspan="2"></th>
    </tr>
    <tr>
        <th>Column1</th>
        <th>Column2</th>
        <th>Column3</th>
        <th>Column4</th>
        <th>Column5</th>
        <th>Column6</th>
    </tr>
</thead>
<tbody>
    <tr>
        <td>Value1</td>
        <td>Value2</td>
        <td>Value3</td>
        <td>Value4</td>
        <td>Value5</td>
        <td>Value6</td>
    </tr>
</tbody>