Hi Marco,
I am working on this but after converting gz to angle i am getting this result
You don't need to convert the gz to angle. Just divide the raw gz value by 131 (for the gyro set at its default of ±250°/s full scale) to get the yaw rate in degrees/s.
To get the bicopter flying initially you only need the gyroscope measuring degrees/s, the calculations shouldn't have anything to do with angle.