With small modification to the article
ASP.Net Nested GridViews – GridView inside GridView with Expand and Collapse feature
You can achieve what you need
<script type="text/javascript">
$("[src*=plus]").live("click", function () {
$("[src*=minus]").each(function () {
$(this).closest("tr").next().remove();
$(this).attr("src", "images/plus.png");
});
$(this).closest("tr").after("<tr><td></td><td colspan = '999'>" + $("[id*=pnlOrders]").html() + "</td></tr>")
$(this).attr("src", "images/minus.png");
});
$("[src*=minus]").live("click", function () {
$(this).attr("src", "images/plus.png");
$(this).closest("tr").next().remove();
});
</script>