The miracle of Purim occurred during a leap year, in the second Adar. The Tur teaches that the 12 months correspond to the 12 tribes. If that is so, who does the second Adar correspond to on a leap year?
Adar links up with Yosef. Indeed, we know the Mazal of Adar is דגים, fish, and Yosef is likened to fish which have no עין הרע.
We know that Adar is the only month that can be a leap month. It therefore comes as no surprise, as the Kedushas Levi points out, that Yosef has two children who are comparable to Shevatim as it says אפרים ומנשה כראובן ושמעון. They correlate with the two Adars.
With this we can appreciate the words Yosef said about Efraim and Menashe, בני הם אשר נתן לי אלה-ים בזה, they are my sons whom Hashem has given me here. The word זה has a numerical value of 12, referring to the 12th month, which can have two months.
