Hey Parth,

Let us conside both the exams separately, 

In Jee Mains:

Duration of Exam: 3 hours

There are 90 questions as 30 questions for each of Chesmitry, Physics and Mathematics.

In BITSAT:

Duration of Exam: 3 hours

It has 150 questions and another EXTRA 12 questions if you have time left. The pattern is as follows:

Chemistry has 40 questions(+4 extra)

Physics has 40 questions(+4 extra)

Mathematics has 45 questions(+4 extra)

English and Logical Reasoning has 25 questions.

It is thereby said that BITSAT is easier than JEE Mains has you only need to have speed whereas in JEE Mains you need to have accuracy and speed and you'd need really good deep knowledge of concepts. Questions in BITSAT are relatively easy and pretty straightforward and you need to just apply the conceps and formulas.

Hope this helps, all the best.