```
# import necessary libraries
import pandas as pd
import numpy as np
# define your series
y_true = pd.Series([1, 2, 3, 4, 5])
y_pred = pd.Series([1.5, 2.5, 3.5, 4.5, 5.5])
# use mean() and square() methods
result = np.mean(np.square(y_true - y_pred))
# print the result
print(f'MSE: {result}')
```