Tooltip for specific tree nodes!

Hi,

How can I implement a tooltip only for particular nodes of a tree!

I started with the example below:

[code]
tree.setItemDescriptionGenerator(new ItemDescriptionGenerator() {

        @Override
        public String generateDescription(Component source, Object itemId, Object propertyId) {
            if (propertyId == null ) {
                return "Node description "+ itemId;
            }
            return null;
        }
    });

[/code]But how to select a particular node within this generateDescription method?

Regards,
Gerard