create table graph (id int, node char, parent char);
insert into graph values (1, 'A', NULL);
insert into graph values (2, 'B', 'A');
insert into graph values (3, 'C', 'A');
insert into graph values (4, 'D', 'B');
insert into graph values (5, 'D', 'C');
insert into graph values (6, 'E', 'D');
insert into graph values (7, 'F', 'E');
insert into graph values (8, 'C', 'F');


