Increase height of dropped separator in QTreeView

Question

I need to increase height of black separator, when I try to drop item between other two. Simple code:

MainWindow::MainWindow(QWidget *parent) :
        QMainWindow(parent),
        ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    ui->treeWidget->setSelectionMode(QAbstractItemView::SingleSelection);
    ui->treeWidget->setDragEnabled(true);
    ui->treeWidget->viewport()->setAcceptDrops(true);
    ui->treeWidget->setDropIndicatorShown(true);
    ui->treeWidget->setDragDropMode(QAbstractItemView::InternalMove);
}