Convert flat recursive array into multidimentional array

Question

I have the following array:

array (size=4)
  0 => 
    array (size=2)
      0 => string '1' (length=1)
      1 => string '5' (length=1)
  1 => 
    array (size=2)
      0 => string '5' (length=1)
      1 => string '2' (length=1)
  2 => 
    array (size=2)
      0 => string '2' (length=1)
      1 => string '9' (length=1)
  3 => 
    array (size=2)
      0 => string '8' (length=1)
      1 => string '11' (length=1)

And I want to convert it into:

array (size=4)
  0 => 
    array (size=2)
      0 => string '1' (length=1)
      1 => 
          array (size=2)
              0 => string '5' (length=1)
              1 => 
                  array (size=2)
                      0 => string '2' (length=1)
                      1 => string '9' (length=1)
  1 => 
    array (size=2)
      0 => string '8' (length=1)
      1 => string '11' (length=1)

So the values with 0 index are above the values with index 1. How can I do that?