How to convert jagged array to 2D array?

I have a file file.txt with the following:

6,73,6,71 
32,1,0,12 
3,11,1,134 
43,15,43,6 
55,0,4,12 

And this code to read it and feed it to a jagged array:

    string[][] arr = new string[5][];
    string[] filelines = File.ReadAllLines("file.txt");
    for (int i = 0; i < filelines.Length; i++) 
    {
        arr[i] = filelines[i].Split(',').ToArray();
    }

How would I do the same thing, but with a 2D array?