how to show a mouse over description of an tree items

Vaadin 6 / 7 / 8
1

i need any body help

2

com.vaadin.ui.Tree.setItemDescriptionGenerator(ItemDescriptionGenerator)

3

i want code for that

4 
tree.setItemDescriptionGenerator(new ItemDescriptionGenerator(){
    public String generateDescription(Component source, Object itemId,
                Object propertyId){
          return "This is my item";
    }
});
5

public String generateDescription(Component source, Object itemId,
Object propertyId)

what arguments i have to pass for above method

6

my objective is when mouse is placed on any item in tree should show it level names