xstream unserialize complex XML to simpler java with Converter

I have surely a problem of understanding of Xstream converter.

I have a pretty complex XML coming from legacy back office application and a just want to convert this one into a simpler java class or a Map with Converter.

1. I do not want to marshal to XML, just unmarshal


2. I do not want to use annotation, just KISS

My XML is like

<root>
    <agent>
        <id>123456789</id>
        <name>GABIN</name>
        <forname>Jean</forname>
        <unit>
            <legacyReference>AA</legacyReference>
            <name>SAN ANTONIO</name>
            <legacyName>SA</legacyName>
            <address>
                <number>1</number>
                <street>Sesam street</street>
                <city>NoWhere</city>
                <legacyID>AAZE-56</legacyID>
            </address>
            <legacyStructurBlablabla>
                <type>OFFICE</type>
                <data>
                    <foo>BAR</foo> 
                </data>
            </legacyStructurBlablabla>
            <...>
        </unit>
        <...> 
    </agent>
</root>

My destination class is very simple

class Agent {
    String id;
    String name;
    String forname;
    String unitName;
    String unitType;
    <...>

}

My main method looks like

xStream = new XStream(new DomDriver());
stream = this.getClass().getClassLoader().getResourceAsStream("data/agent.xml") ;
xStream.alias("root", Map.class);
xStream.alias("agent", Agent.class);
xStream.registerConverter(new ResultConverter());
xStream.registerConverter(new AgentConverter());
xStream.ignoreUnknownElements();

Object obj = xStream.fromXML(stream);

I don't understand how to step down in favor of another converter.

public class ResultConverter implements Converter {

...


public Object unmarshal(HierarchicalStreamReader reader,
        UnmarshallingContext context) {
    Map<String, Object> agents = new HashMap<String, Object>();
    while( reader.hasMoreChildren() ) {
        reader.moveDown();
        // HOW I DO TO STEP DOWN IN FAVOR OF Agent CONVERTER ?
        reader.moveUp();
    }
    return agents;
}

I didn't see Xstream scrolled dow the thierarchy to activate my AgentConverter.

I surely missing the point