Calculation View Hierarchy

I have a calculation view and in it I have a date hierarchy which is working fine.

I now want to add a simple three level org hierarchy. I have three columns which I add. I declare the hierarchy as node style = name only and hierarchy type = level hierarchy. However I can't validate. IT gives an error please select the level attribute in the hierarchy TEAM STRUCT. What is a level attribute? why should I need one? How would I add it?

Thanks

Cliff