graph LR
subgraph level1
    subgraph level2
        subgraph level3
            A
        end
    end
end
---
+---------------+
|    level1     |
|               |
|               |
| +-----------+ |
| |  level2   | |
| |           | |
| |           | |
| | +-------+ | |
| | |level3 | | |
| | |       | | |
| | |       | | |
| | | +---+ | | |
| | | |   | | | |
| | | | A | | | |
| | | |   | | | |
| | | +---+ | | |
| | |       | | |
| | +-------+ | |
| |           | |
| +-----------+ |
|               |
+---------------+
