Nattable tree hierarchy change to show children modules first

Question

I want a particular desired behavior for my Nattable tree structure. In the following diagram, contents of Row no 36, 37 are children of content in Row 20.

Row 21, 23, 23 … 34 are in turn children of Row 20.

Row 22 is a child of Row 21. (you could say it is grandchild of 20)

I want Row 36, 37 to be shown first ie. In place of Row 21 and so on, that is I want to change the order in which it is shown as a child of Row 20.

I am currently using a treelist implementation to render my data in the Nattable.

My current nattable:

 private List<ISectionInfo> getFlatList(List<ISectionInfo> inputList)
 {
     List<ISectionInfo> flatList = new ArrayList<ISectionInfo>();

     for (ISectionInfo node : inputList)
     {

         if (node instanceof SectionInfo) 
         {
             SectionInfo secNode = (SectionInfo) node;

             if (!hasChildren(secNode))
             {
                 flatList.add(secNode);
                 flatList.addAll(secNode.getModuleInfoList());

             }
             if (hasChildren(secNode))
             {
                 flatList.addAll(secNode.getModuleInfoList());
                 flatList.add(secNode);

                 for (ISectionInfo iternode : secNode.getChildren())
                 {
                     flatList.addAll(((SectionInfo) iternode).getModuleInfoList());
                     flatList.add(iternode);

                 }

             }
         }

     }

     return flatList;

 }