GXT中如何在TreePanle中的节点实现不同图标

如题.我现在有一个tree,需要更具tree的内容不同来设定不同的节点图标.这个要如何实现.期望高手能指点下.最好能有个简单的实例代码.

...
TreeStore treeStore = new TreeStore();
TreePanel treePanel = new TreePanel(treeStore);
treePanel.setIconProvider(new TreeIconProvider());

...
public class TreeIconProvider implements ModelIconProvider {
private ImageBundleImplement icon = GWT.create(ImageBundleImplement.class);

@Override
public AbstractImagePrototype getIcon(BaseModel model) {
    String type = model.get("type");
    if ("XX1".equals(type)) {
        return icon.img1();
    } else if ("XX2".equals(type)) {
        return icon.img2();
    } 
    return img3;
}

}
...
不知道是否清楚