Hi Kaan,

if you like to control the Attiny with a receiver, you don't need the function "push button" from the arduino library. The function "push button" from the arduino library only shows you, if a connected button is pushed or not. So the function returns a one (while button is pushed) or a zero (while button is not pushed). For controlling the microcontroller with a radio controlled receiver, it is necessary to encode the pulse-width-signal (PWM), which is generated from the receiver.
Try to measure the pulse by using a timer. Start measuring at the rising edge and stop the timer or read back the timer value at the falling edge.

regards

Hendrik