Trees do not really map well to relational databases.
The most obvious way of storing them is like:
Tree
| ID | Parent ID | Name |
| 3 | 1 | Countries |
| 4 | 3 | Belgium |
| 5 | 3 | Netherlands |
| 6 | 3 | Germany |
| 7 | 5 | Business |
| 8 | 5 | Economy |
| ID | Parent ID | Name |
| 3 | 1 | Countries |
| 4 | 3 | Belgium |
| 5 | 3 | Netherlands |
| 6 | 3 | Germany |
| 7 | 5 | Business |
| 8 | 5 | Economy |