Hi dear hope you are doing well. Dual degree in BTech means you will get a b tech as well as Mtech in that particular field for example if you take dual degree in a computer science engineering then you will get both the BTech and Mtech in computer science engineering. There are many colleges in India which provide dual degree courses and the eligibility criteria for the cutoff for the dual degree courses are slightly less than that of single degree that is BTech. So if you are somehow unable to get admission in BTech you can definitely take the dual degree course. Hope this will help you good luck.

Hello,

So, basically Dual degree with respect to B.tech means that you will be getting your B.Tech anand M. Tech degree separately.You will get a B. Tech Degree after 4 year course and then a M. Tech Degree after 2 year course.
What you will get with dual degree is the fees of M.Tech will be same when you started your B Tech degree initially.
There is also a integrated course in which you can do B.tech+M.tech in 5 years.There are many universities in India that offer these courses.You  can checkout the names of the colleges  from the link below :

https://engineering.careers360.com/colleges/list-of-dual-degree-engineering-colleges-in-india