I have QTreeView with QFileSystemModel.

    treeView=new QTreeView;
    treeView->header()->hide();
    fsModel=new QFileSystemModel;
    fsModel->setRootPath(QDir::rootPath());
    fsTreeView->setModel(fsModel);

I have 2 logical disks C and E. When I expand disk C in treeview files are after folders. When I expand disk E - files and folders are mixed, they are all sorted alphabeticaly by name.