tree grid help

I trying to use treegrid, first I catch all the code in demo and put in my app, but the tree grid don`t show the childs, he only show the first time.. 

so now I tryng to create my ow DemoContainer just like this:

public class DemoContainer extends HierarchicalContainer implements Collapsible, Measurable {

    static final String PROPERTY_NAME = "Name";
    static final String PROPERTY_HOURS = "Hoursdone";

    public DemoContainer() {
        super.addContainerProperty("Name", String.class, "");
        super.addContainerProperty("Hoursdone", String.class, "");
    }

    public Item addItem(TbCategoriaReceitaDespesa categoria){
        Item r =  super.addItem(categoria);
        r.getItemProperty("Name").setValue(categoria.getNmDespesaCategoria());
        r.getItemProperty("Hoursdone").setValue(categoria.getIdDespesaCategoria());
        super.setChildrenAllowed(r,true);
        return r;
    }

    public void addChildren(TbCategoriaReceitaDespesa categoria, TbCategoriaReceitaDespesa parent){
       Item r = addItem(categoria);
       super.setParent(categoria,parent);

    }

    @Override
    public void setCollapsed(Object o, boolean b) {
        System.out.println("entrou 1");
    }

    @Override
    public boolean isCollapsed(Object o) {
        System.out.println("entrou 2");
        return true;
    }

    @Override
    public int getDepth(Object o) {
        return 0;
    }
}

But in my Code I can`t add children he put below the parent and not inside.

how can I fix this?

tks