thanks for your support. This will work. Now I have another problem. And it seems to be a performance problem. My employee data source has over 1M lines and more than 25 columns. Is there another way to get a such hierarchy?
At that size you might see some improvements with having it in a database.
Alternatively, if you don't need to use all of the 25 columns for both employee and manager you can hide them so they're not used in processing.