oracle存储过程中用utl_file包生成xml文件内容追加问题

我现在生成xml，使用utl_file.fopen();是的A模式来追加文件内容，但是每次追加后又重新生成一个根节点，如下：
<?xml version="1.0"?>
<ROWSET>
 <ROW>
  <UNIT>【901103001】贵阳市人民政府办公厅本级</UNIT>
  <SUBJECT>【501210301】行政运行(政府办公厅)</SUBJECT>
  <PROJECT>商品和服务支出</PROJECT>
  <SUMMARY>筑财预[2013]号</SUMMARY>
  <TARGETAMOUNT>5000000</TARGETAMOUNT>
  <PAYMENT>1500000</PAYMENT>
  <TARGETCURRENT>5000000</TARGETCURRENT>
  <PAYMENTCURRENT>3500000</PAYMENTCURRENT>
  <REALITYAMOUNT>3500000</REALITYAMOUNT>
 </ROW>
</ROWSET>
<ROWSET>
 <ROW>
  <UNIT>【901103001】贵阳市人民政府办公厅本级</UNIT>
  <SUBJECT>【501210301】行政运行(政府办公厅)</SUBJECT>
  <PROJECT>对个人各家庭的补助支出</PROJECT>
  <SUMMARY>筑财预[2013]号</SUMMARY>
  <TARGETAMOUNT>2997351</TARGETAMOUNT>
  <PAYMENT>500000</PAYMENT>
  <TARGETCURRENT>2997351</TARGETCURRENT>
  <PAYMENTCURRENT>2497351</PAYMENTCURRENT>
  <REALITYAMOUNT>2497351</REALITYAMOUNT>
 </ROW>
</ROWSET>
我想问的是：现在怎么实现把追加的内容加入到<ROWSET>根节点下，如下：
<?xml version="1.0"?>
<ROWSET>
 <ROW>
  <UNIT>【901103001】贵阳市人民政府办公厅本级</UNIT>
  <SUBJECT>【501210301】行政运行(政府办公厅)</SUBJECT>
  <PROJECT>商品和服务支出</PROJECT>
  <SUMMARY>筑财预[2013]号</SUMMARY>
  <TARGETAMOUNT>5000000</TARGETAMOUNT>
  <PAYMENT>1500000</PAYMENT>
  <TARGETCURRENT>5000000</TARGETCURRENT>
  <PAYMENTCURRENT>3500000</PAYMENTCURRENT>
  <REALITYAMOUNT>3500000</REALITYAMOUNT>
 </ROW>
 <ROW>
  <UNIT>【901103001】贵阳市人民政府办公厅本级</UNIT>
  <SUBJECT>【501210301】行政运行(政府办公厅)</SUBJECT>
  <PROJECT>对个人各家庭的补助支出</PROJECT>
  <SUMMARY>筑财预[2013]号</SUMMARY>
  <TARGETAMOUNT>2997351</TARGETAMOUNT>
  <PAYMENT>500000</PAYMENT>
  <TARGETCURRENT>2997351</TARGETCURRENT>
  <PAYMENTCURRENT>2497351</PAYMENTCURRENT>
  <REALITYAMOUNT>2497351</REALITYAMOUNT>
 </ROW>
</ROWSET>
请大家知道的帮帮忙。先谢了