Please solve the programming task below using a self-contained code snippet in a markdown code block.

You are given two strings word1 and word2. Merge the strings by adding letters in alternating order, starting with word1. If a string is longer than the other, append the additional letters onto the end of the merged string.
Return the merged string.
 
Please complete the following python code precisely:
```python
class Solution:
    def mergeAlternately(self, word1: str, word2: str) -> str:
```