Why is the standard time of bangladesh half hour ahead of India?

India spreads along two distinctive time zones + UTC5:00 and UTC+6:00. In any case, India needed to proceed with a similar time all through the entire nation and hence thought of UTC+5:30 which is the normal of the above. In spite of the fact that this works decently pleasantly for the various parts of India, it doesn't function admirably for the northeastern states.