TreeGrid LoadDataOnDemand Display always Folders but no leaves

[jose.hello]

Hello,

Subject:
How to set folders and leaves nodes using server datasource .ds.xml ?

I use Smartgwt 3.0p power

I load a treeGrid with an datasource and LoadDataOnDemand set to true.

Of course all nodes are folders.

I have see setIsFolder(false) methods but I don't know how to setup my datasource

I have see that :
DataSourceBooleanField isFolderField = new DataSourceBooleanField("isFolder", "isFolder");
isFolderField.setHidden(true);
isFolderField.setRequired(true);

But It's pure Java code and my datasource is on a ds.xml file.

I have try this : but i's doesn't work
<DataSourceBooleanField name="isFolder" type="boolean" hidden="true" required="true" />

How to say to the server that pass to the client if a node is an folder or a leaf ?

How to setup my datasource for do this ?

Thanks,

[jose.hello]

Have everybody a standalone sample with Datasource ?