Given the root of a binary tree and an integer `targetSum`, return `true` if the tree has a **root-to-leaf** path such that adding up all the values along the path equals `targetSum`. A leaf is a node with no children.
**Note:** The tree is given as a level-order array where the node at index `i` has its left child at index `2*i + 1` and its right child at index `2*i + 2`, with `null` for missing nodes (trailing positions may be omitted).
For example, `[5, 4, 8, 11, null, 13, 4, 7, 2, null, null, null, null, null, 1]` represents:
```
5
/ \
4 8
/ / \
11 13 4
/ \ \
7 2 1
```
The path 5 -> 4 -> 11 -> 2 sums to 22.