support incremental lazy loading for child nodes in QTreeView

QTreeView is calling canFetchMore() only when expand an item & after that if I scroll down canfetchMore() is not at all getting called in order to load more children in case if parent item has more child's . This is happening for the non root item only, canFetchMore() is working as expected for root Item.

I had posted in Qt forum regarding this : http://www.qtcentre.org/threads/63911-MVC-canFetchMore()-is-not-working-as-expected