web/web_export_view/static/src/xml/web_export_view_template.xml

<?xml version="1.0" encoding="UTF-8"?>

<templates id="template" xml:space="preserve">
<t t-name="WebExportTreeViewXls">
    <div class="o_cp_sidebar btn-group btn-group-sm">
        <button class="btn btn-default export_treeview_xls" type="button" title="Export xls">
            <i t-translation="off" class="fa fa-file-excel-o"></i>
        </button>
    </div>
</t>
</templates>