@Entity
public class Employee {
	@Id
	private long id;
	private String firstName;
	private String lastName;
	@OneToMany(mappedBy = "parent", orphanRemoval = true, cascade = { CascadeType.ALL })
	@CascadeOnDelete
	private List<Employee> children;
	@ManyToOne
	private Employee parent;
}

CREATE TABLE EMPLOYEE (ID BIGINT NOT NULL, FIRSTNAME VARCHAR(255), LASTNAME VARCHAR(255), PARENT_ID BIGINT, PRIMARY KEY (ID))
ALTER TABLE EMPLOYEE ADD CONSTRAINT FK_EMPLOYEE_PARENT_ID FOREIGN KEY (PARENT_ID) REFERENCES EMPLOYEE (ID)