UiBinder Placeholder

how can I create a placeholder with开发者_如何学C in the UiBInder, to later fill it with e.g. a Tree element? (Like the Flextable, but simpler).

Regards, Stefan

<g:SimplePanel ui:field="panelForTree" />

Then, in Java:

@UiField protected SimplePanel panelForTree;

...

panelForTree.setWidget(theTreeYouMadeLater);