@Entity
@NoSql(dataFormat = DataFormatType.MAPPED)
public class MySystem implements Serializable{

    @ElementCollection
    List<Folder>    folders    = new ArrayList<Folder>();
}

@Embeddable
@NoSql(dataFormat = DataFormatType.MAPPED)
public class Folder implements Serializable {

    @ElementCollection
    List<Folder>    subFolders    = new ArrayList<Folder>();
}