Considering the Tree as binary

```
a
/\
b c
/ / \
d e f
/ \ \
g h p
\
k
```

The longest leaf to leaf path would be k-h-d-b-a-c-f-p i.e of length 8.

- Calculate the diameter at each node (assuming node as a root of the tree)
- Diameter is the height of left subtree + height of right subtree + 1.
- Pick the highest diameter amongst all.