prefab not being instanced if its added as a child of another prefab,Why adding transform to instanciate breaks the code?

I have this code executed in a prefab called Wheel. This prefab has to instanciate another prefab called slice and add it as a child.

This works: GameObject slice = Instantiate<GameObject>(sliceToCreate);

It properly instanciates the slice, its added to the hierarchy and shown in the scene BUT its not added as a children. To add it , as far as a I know I can add transform as a second parameter.

 GameObject slice = Instantiate<GameObject>(sliceToCreate, transform);

But with this line, the objects are not instanciated, or at least, ar not shown in the hierarchy and scene.

Even if I try slice.transform.parent = transform; after it, it breaks. ("setting the parent of a transform which resides in a prefab is disabled to prevent data corruption")