XML : Append element in xml file in opencv using cpp

I am trying to append a new element in my opencv xml file which already has one element as below

  <?xml version="1.0"?>  <opencv_storage>  <acc type_id="opencv-ml-ann-mlp">  ...  </_></weights></acc>  </opencv_storage>    

I am trying to append one more element called micr as below

  <?xml version="1.0"?>  <opencv_storage>  <acc type_id="opencv-ml-ann-mlp">  ...  </_></weights></acc>    <micr type_id="opencv-ml-ann-mlp">  ...  </_></weights></micr>  </opencv_storage>    

But what I am getting is

  <?xml version="1.0"?>  <opencv_storage>  <acc type_id="opencv-ml-ann-mlp">  ...    <micr type_id="opencv-ml-ann-mlp">  ...  </_></weights></micr></_></weights></acc>  </opencv_storage>    

I am using cv::FileStorage from opencv.

I want to know what is wrong with ::app and if there is any alternative to achieve this. Thanks in advance!