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

You are given a 2D integer array intervals where intervals[i] = [starti, endi] represents all the integers from starti to endi inclusively.
A containing set is an array nums where each interval from intervals has at least two integers in nums.

For example, if intervals = [[1,3], [3,7], [8,9]], then [1,2,4,7,8,9] and [2,3,4,8,9] are containing sets.

Return the minimum possible size of a containing set.
 
Please complete the following python code precisely:
```python
class Solution:
    def intersectionSizeTwo(self, intervals: List[List[int]]) -> int:
```