SilverStripe\Assets\Folder:
  folder1:
    Name: folder
    Title: folder
  folder2:
    Name: subfolder
    Title: subfolder
    Parent: =>SilverStripe\Assets\Folder.folder1

SilverStripe\Assets\File:
  example_file:
    Name: example.pdf
    Parent: =>SilverStripe\Assets\Folder.folder2

SilverStripe\Assets\Image:
  example_image:
    Name: HTMLEditorFieldTest_example.jpg
    Parent: =>SilverStripe\Assets\Folder.folder2