public class GroupParent {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "id")
    private Long id;

    @Column(name = "code", length = 128, unique = true)
    private String code;

    @Column(name = "name", length = 512)
    private String name;

    @JsonManagedReference
    @OneToMany(mappedBy = "parentGroup", cascade = CascadeType.ALL)
    @OrderColumn(name="id")
    Set<Parent> parents = new HashSet<>();
}

public class Parent {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "id")
    private Long id;

    @JsonBackReference
    @ManyToOne
    @JoinColumn(name = "group_id")
    private GroupParent parentGroup;

    @Column(name = "code", length = 128, unique = true)
    private String code;

    @Column(name = "name", length = 512)
    private String name;

    @JsonManagedReference
    @OneToMany(mappedBy = "parent", cascade = CascadeType.ALL)
    @OrderColumn(name="id")
    Set<Child> childs = new HashSet<>();
}

public class Child {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "id")
    private Long id;
    
    @JsonBackReference
    @ManyToOne
    @JoinColumn(name = "parent_id")
    private Parent parent;

    @Column(name = "code", length = 128, unique = true)
    private String code;

    @Column(name = "name", length = 512)
    private String name;

   @Column(name = "start_date")
    private LocalDateTime startDate; 

    @Column(name = "end_date")
    private LocalDateTime endDate;
}