Is this function in O(n) time?

def power(base, n): #any number raised to zero is one if (n == 0): return 1 #if the number is even elif (int(n % 2) == 0): return (power(base, int(n / 2))) * power(base, int(n / 2)) #if the number is odd else: return (base * power(base, int(n / 2))) * power(base, int(n / 2)) print("Result of 2 raised to the 20th:", power(-2, 2))

If so, what is the recurrence relation so I can use master theorem to calculate the running time?