C# Imperative MergeSort

ImperativeMergeSort.cs

public class Imperative
{
    public int[] MergeSort(int[] array)
    {
        if (array.Length <= 1) return array;
        
        var (arrayA, arrayB) = Split(array);
        var sortedA = MergeSort(arrayA);
        var sortedB = MergeSort(arrayB);
        var mergedArray = Merge(sortedA, sortedB);
        return mergedArray;

    }

    public (int[], int[]) Split(int[] array)
    {
        var arrayA = new int[array.Length / 2];
        Array.Copy(array, 0, arrayA, 0, arrayA.Length);
        var arrayB = new int[array.Length - arrayA.Length];
        Array.Copy(array, arrayA.Length, arrayB, 0, arrayB.Length);

        return (arrayA, arrayB);
    }

    private int[] Merge(int[] arrayA, int[] arrayB)
    {
        var merged = new int[arrayA.Length + arrayB.Length];

        (int a, int b) = (0, 0);
        while (a < arrayA.Length && b < arrayB.Length)
        {
            if (arrayA[a] < arrayB[b])
            {
                merged[a + b] = arrayA[a];
                a++;
            }
            else
            {
                merged[a + b] = arrayB[b];
                b++;
            }
        }

        for (int i = a; i < arrayA.Length; i++)
        {
            merged[i + b] = arrayA[i];
        }

        for (int i = b; i < arrayB.Length; i++)
        {
            merged[a + i] = arrayB[i];
        }

        return merged;
    }
}