HowTo draw QTreeWidgetItem with different style?

Here is the main problem: I'm using QTreeWidget class as a main tree, which must show me this tree structure:

[Today]
   [Row1]
   [Row2]
      [SubRow21]
      [SubRow22]
   [Row3]
[Yesterday]
   [Row4]
      [SubRow41]
[etc]

With Qt Designer I have set this style sheet code:

QTreeWidget#treeWidget::item
{
    height: 24px;    
    border: none;    
    background-position: bottom left;   
    background-image: url(:/backgrounds/images/backgrounds/row_back.png);
}
QTreeWidget#treeWidget::item:selected
{
    color: #000000;    
    background-position: bottom left;
    background-image: url(:/spreadsheet/images/spreadsheet/row_back_selected.png);
}

And all items drawn with the *row_back.png* background image, but I need to draw another background image to [Today] and [Yesterday] rows! For these purposes I had inherit QStyledItemDelegate class, but don't know methods, to reset style to new background image:

void MyColumnDelegate::paint( QPainter* painter, const QStyleOptionViewItem& option, const QModelIndex& index ) const
{
     QStyleOptionViewItemV4 op = option;

     if( isPeriod( index ) )
     {
          // here I heed to change background image!!!

          //QStyle* style = op.widget ? op.widget->style() : QApplication::style();
          //style->drawControl( QStyle::CE_ItemViewItem, &op, painter, op.widget );

          //QRect backgroundRect( option.rect.x() + 5, option.rect.y() + 5, 18, 18 );
          //style->drawItemPixmap( painter, backgroundRect, Qt::AlignCenter, QPixmap( SOME_PIC ) );    
          //QStyledItemDelegate::paint( painter, op, index );

          return;
     }

     op.text = "";
     QStyle* style = op.widget ? op.widget->style() : QApplication::style();
     style->drawControl( QStyle::CE_ItemViewItem, &op, painter, op.widget );  

     QModelIndex dataIndex = index.model()->index( index.row(), ePosChain, index.parent() );
     LetterInfo data = index.model()->data( dataIndex, PackageDataRole ).value< LetterInfo >();

     switch( data.document_.state_ )
     {
     case( eStateSignedByOwner ):
          painter->drawPixmap( getPos( op, index, QPixmap( IMAGE2 ) ), QPixmap( IMAGE2 ) );
          break;
     case( eStateSignedByHost ):
          painter->drawPixmap( getPos( op, index, QPixmap( IMAGE1 ) ), QPixmap( IMAGE1 ) );
          break;
     }

     painter->drawText( getTextPos( op, index ), data.text );
}

Any help?

Thanks!

Solved with this code:

if( isPeriod( index ) )
     {
          QPixmap pixmap( PERIOD_ROW_BACKGROUND );
          painter->drawPixmap( op.rect, pixmap, pixmap.rect() );

          return;
     }