将flat recursive数组转换为多维数组

Question

我有以下数组：

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)

我想将其转换为：

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)

所以0索引的值高于索引1的值。我该怎么做？