Primefaces Subtable inside another subtable - jsf

Question

Can we use a simple subtable inside another subtable?
I tried to use like this, but html is not generated.
I can get this done by using ui:repeat or p:dataGrid, but the issue is that the generated data table must be able to be exported to Excel & PDF with p:dataExporter. That is not supported in primefaces if we use it with anything other than dataTable.
Please help.
<p:dataTable id="tbl" value="#{storeReportsTransfer.drows}" var="i" >
<f:facet name="header">
<h:outputLabel value="Department Issue Report "/>
<h:outputLabel value="#{storeReportsTransfer.fromDepartment.name}"/>
</f:facet>
<p:columnGroup type="header">
<p:row>
<p:column headerText="Department" />
<p:column headerText="Category" />
<p:column headerText="Item" />
<p:column headerText="Rate" />
<p:column headerText="Total" />
</p:row>
</p:columnGroup>
<p:subTable value="#{i.categoryBillRows}" var="cbr" >
<f:facet name="header">
<h:outputText value="#{i.department.name}" />
</f:facet>
<p:column >
</p:column>
<p:column>
<h:outputText value="#{cbr.category.name}" />
</p:column>
<p:column>
<p:subTable value="#{cbr.itemBillRows}" var="ibr" >
<p:column>
<h:outputText value="#{ibr.item.name}" />
</p:column>
<p:column>
<h:outputText value="#{ibr.bill.netTotal}" />
</p:column>
<p:column>
<h:outputText value="#{ibr.bill.grantTotal}" />
</p:column>
</p:subTable>
</p:column>
<p:columnGroup type="footer">
<p:row>
<p:column footerText="Totals: " style="text-align:right"/>
<p:column footerText="#{cbr.bill.netTotal}" />
</p:row>
</p:columnGroup>
</p:subTable>
</p:dataTable>