Converting code for ATTINY85 to ATMEGA2560. Pin change interupts

I have code that compiles correctly for an ATTINY85 board using the ARDUINO IDE but I don't have an ATTINY85 board. I have an Arduino Mega ATMEGA2560 and when I select this board in the Arduino IDE the code does not compile and throws this error message

sketch_feb21a:216:3: error: 'GIMSK' was not declared in this scope

   GIMSK |= _BV(PCIE);                     // Enable Pin Change Interrupts

   ^

sketch_feb21a:216:16: error: 'PCIE' was not declared in this scope

   GIMSK |= _BV(PCIE);                     // Enable Pin Change Interrupts

                ^

sketch_feb21a:217:3: error: 'PCMSK' was not declared in this scope

   PCMSK |= _BV(PCINT2);                   // Use PB3 as interrupt pin

   ^

exit status 1
'GIMSK' was not declared in this scope

Here is the code snippet that throws the error

void sleep()
{
  GIMSK |= _BV(PCIE);                     // Enable Pin Change Interrupts
  PCMSK |= _BV(PCINT2);                   // Use PB3 as interrupt pin
  ADCSRA &= ~_BV(ADEN);                   // ADC off
  set_sleep_mode(SLEEP_MODE_PWR_DOWN);    // replaces above statement

  MCUCR &= ~_BV(ISC01);
  MCUCR &= ~_BV(ISC00);       // Interrupt on rising edge
  sleep_enable();                         // Sets the Sleep Enable bit in the MCUCR Register (SE BIT)
  sei();                                  // Enable interrupts
  sleep_cpu();                            // sleep

  cli();                                  // Disable interrupts
  PCMSK &= ~_BV(PCINT2);                  // Turn off PB3 as interrupt pin
  sleep_disable();                        // Clear SE bit
  ADCSRA |= _BV(ADEN);                    // ADC on

  sei();                                  // Enable interrupts
}



ISR(PCINT0_vect) {
   /*noInterrupts();
   while (digitalRead(BUTTON_PIN) == LOW);

   delay(50);
   while (digitalRead(BUTTON_PIN) == LOW);
   playTrack(1 + (curTrack++ % 2));
   delay(400);

   interrupts();*/

}