Why there is no much change in the incremental backup size of level 0 and level 1
But in my db after level 0 full backup, level 1 backup is also taking
  the almost same backup size of level 0.


Verify if the backup generated in level 0 exists there in the location, while level 1 backup occurs.

The level 0 backup might have got deleted or removed from the location. This might be the reason for this issue.