Dear Aspirant,

As for the syllabus part, there is some similarity between the bank PO exam and CAT exam but in fact, they both are quite different exams. In CAT both the level and complexity is a bit higher. 

For the preparation part, yes you can prepare for both exams side by side, but it is that you have to study some more variety of questions for CAT. Moreover, you have to set your priority. If you are serious about the CAT exam then you have to give more hours to it. Give some free mocks available to first identify your string and weak areas and then work on your weak areas more alongside the bank preparation.

MOCKS are very very important and do not skip them.

Here are few links for you:-

https://bschool.careers360.com/articles/cat-preparation-2019-how-prepare-for-cat-without-coaching

Thanks.