Hello Kamal!

That is a very good option!

For becoming an IAS officer after CSE you have to appear in UPSC civil services exam after completing your degree. It will be better if you grasp your course very well around those 4 years so that the papers related to your course will become easier to clear.

Now you can take a drop as well for your preparation or you can prepare from beginning of your degree or during final year of your b.tech for other paper of Civil Services exam like Aptitude and reasoning. 

Make sure to don't harm your subject studies during your degree.

All the best!