In the case of a mutual savings bank not having capital stock represented by shares, authorized under State law to engage in the business of issuing life insurance contracts, and which conducts a life insurance business in a separate department the accounts of which are maintained separately from the other accounts of the mutual savings bank, there shall be imposed in lieu of the taxes imposed by section
11 or section
1201
(a), a tax consisting of the sum of the partial taxes determined under paragraphs (1) and (2):