XML: multiple values into Multi-Field

I have a XML that has multiple occurrances of the same item like this:

<root>
<person>
<ref value="A" />
<ref value="B" />
<ref value="C" />
</person>
<person>
<ref value="A" />
<ref value="D" />
</person>
<person>
<ref value="E" />
<ref value="H" />
</person>
...
</root>

I want to migrate the ref-values as sub-values into a field that allows multiple values.

Person1

References
A
B
C

etc.

I can up set field_reference with the xpath "ref/@value", but do to a loop in fetchNextRow() in

class Xml extends DataParserPluginBase implements ContainerFactoryPluginInterface

I would only get the last value

Any suggestions on how to fix this would be welcome.