|1|
    / \
   1   1
  /     \
|2|     |4|
 |       |
 3       2
 |       |
|3|     |5|
 \      /
  1    1
   \  /
   |6|
    |
    1
    |
   |7|


7 6 1 7
1 2 1
1 4 1
2 3 3
3 6 1
4 5 2
5 6 1
6 7 1