How to insert n DataFrame to another every nth row in Pandas?

For example, I have an DataFrame A as following

A
0
1
2

Now I want to insert every 2 rows in DataFrame B into A every 1 row and B is as following

B
3
3
4
4
5
5

finally I want

A
0
3
3
1
4
4
2
5
5

How can I achieve this?