SQL & PL/SQL :: Roll-up Tree With Parent-child Identifiers?

There is table:

Column A | Column B |
X | X |
X | Y |
Y | X |
Y | Y |

I have selected view with "group by rollup":

ID | Column A | Column B |
1 | | |
2 | X | |
3 | Y | |
4 | X | X |
5 | X | Y |
6 | Y | X |
7 | Y | Y |

Now I want to display it in client app like a tree.So, I need create ID's of parents in child rows, like this:

ID | Parent ID | Column A | Column B |
1 | | | |
2 | 1 | X | |
3 | 1 | Y | |
4 | 2 | X | X |
5 | 2 | X | Y |
6 | 3 | Y | X |
7 | 3 | Y | Y |