Get the union of 2 series having different root items in Websphere TX

Question

Here is a sample of my problem. I have the following typetree :

Root
 |-Text(item)
 |-Texts(group, delimited, literal separator=<NEXT>, components=Text[1:s])

I have 3 cards :

serie1 (type=Texts), rule =clone("test", 3)
serie2 (type=Texts), rule =clone("test", 3) 
union (type=Texts), rule =? 

How can I get the union to contain both the values from serie1 and serie2 ?

If possible not using a RUN