Multiple Elements in ElementMaker in lxml python

I wish to use ElementMaker in lxml to build an xml representation of an excel spreadsheet with the corresponding nesting. I would like

<excelbook>
  workbook info
  <excelsheet>
      <sheetname>Sheet1</sheetname>
      <exceltable>
        <numrows>10</numrows>
        <numcols>13</numcols>
      </exceltable>
      <exceltable>
        <numrows>10</numrows>
        <numcols>13</numcols>
      </exceltable>
    </excelsheet>
    <excelsheet>
      <sheetname>Sheet2</sheetname>
      <exceltable>
        <numrows>10</numrows>
        <numcols>13</numcols>
      </exceltable>
      <exceltable>
        <numrows>10</numrows>
        <numcols>13</numcols>
      </exceltable>
  </excelsheet>
</excelbook>

My python code looks like the following

    for excelSheet in excelBook.excelSheets:

        for excelTable in excelSheet.excelTables:

            exceltable = E.exceltable(
                E.num_rows(str(excelTable.num_rows)),   
                E.num_cols(str(excelTable.num_cols)),
                )

        excelsheet = E.excelsheet(
                exceltable,
                E.sheetname(excelSheet.sheetName),
                )

        excelbook = E.excelbook(
        excelsheet,
        E.bookname(fullpathname),
        E.numSheets(str(excelBook.numSheets))) 

        root = E.XML(excelbook)

The problem is that I can only nest one sheet inside each book and one table inside each sheet. How do I change the code to allow multiple sheets in each book and multiple tables inside each sheet.