help needed with custom drawing in SWT.Tree

Hello,

In the tiny piece of code below, I am not able to figure out whats
wrong with the custom drawing of code.
I want it to use for displaying text that spans multiple columns
(starting from column 0)

Thanks a lot in advance.
Techie

class test {

    Display display;
    Shell shell;

    public test () {
        display = new Display ();
        shell = new Shell (display);

        text_spanning_all_columns ();

        shell.pack ();
        shell.open ();
        while (!shell.isDisposed()) {
            if (!display.readAndDispatch ()) display.sleep ();
        }
        display.dispose ();
    }

    void text_spanning_all_columns () {
        shell.setLayout (new FillLayout());
        final Tree table = new Tree(shell, SWT.MULTI | SWT.FULL_SELECTION);
        table.setHeaderVisible(true);
        int columnCount = 4;
        for (int i=0; i<columnCount; i++) {
            TreeColumn column = new TreeColumn(table, SWT.NONE);
            column.setText("Column " + i);
        }
        int itemCount = 8;
        for (int i = 0; i < itemCount; i++) {
            TreeItem item = new TreeItem(table, SWT.NONE);
            item.setText(0, "item "+i+" a");
            item.setText(3, "item "+i+" d");
            TreeItem subItem = new TreeItem (item, SWT.NONE);
        }
        /*
         * NOTE: MeasureItem, PaintItem and EraseItem are called repeatedly.
         * Therefore, it is critical for performance that these methods be
         * as efficient as possible.
         */
        final String string = "text that spans two columns and much much
more";
        GC gc = new GC(table);
        final Point extent = gc.stringExtent(string);
        gc.dispose();
        final Color red = display.getSystemColor(SWT.COLOR_RED);
        Listener paintListener = new Listener() {
            public void handleEvent(Event event) {
                switch(event.type) {
                    case SWT.MeasureItem: {
                        TreeItem item = (TreeItem) event.item;
                        if (item.getParentItem() != null) {
                            //event.width = extent.x/2;
                            //event.height = Math.max(event.height, extent.y + 2);
                        }
                        break;
                    }
                    case SWT.PaintItem: {

                        TreeItem item = (TreeItem) event.item;
                        if (item.getParentItem() != null) {
                            int offset = 0;
                            for (int i=0; i<event.index; i++)
                                offset += table.getColumn(i).getWidth();

                            event.gc.setForeground(red);
                            int y = event.y + (event.height - extent.y)/2;
                            event.gc.drawString(string, event.x - offset, y, true);
                        }
                        break;
                    }
                }
            }
        };
        table.addListener(SWT.MeasureItem, paintListener);
        table.addListener(SWT.PaintItem, paintListener);
        for (int i = 0; i < columnCount; i++) {
            table.getColumn(i).pack();
        }
    }
}

public class abc {

    public static void main(String [] args) {
        new test();
    }
}