To keep consistency with: EZP-29026

Preconditions:

Content item with sub-items created. They are all assigned to Standard section.

Steps:

1. Go to Admin/Sections
2. Click assign button next to Media section
3. Select Content item from preconditions and Confirm

Actual result:

Only parent CI is moved to Media section.

Expected result:

Whole subtree should be moved to Media section.