How to use for each subgraph in dataflow from geometry collection

Hello, I’m working on chaos destruction by dataflow and I want to fracture each bone by their own boundbox instead of using boundingbox from all of them, as the picture shows:

It works well, but I have many bones (at least 20) and I think I need a loop to help me. However, the loop seems not effect:

What’s wrong in it? Could anyone help me? Thank you very much