How to merge one array elements in laravel?

i am new in laravel. i want to merge 2 multidimansional array in one array. i am using array_merge function but isn't work. i want merge array[0] position values and array[1] position values.

here is my current array look like this

Array
(
  [0] => Illuminate\Support\Collection Object
      (
          [items:protected] => Array
              (
                  [0] => stdClass Object
                      (
                          [product_id] => 2
                          [sale_datetime] => 2018-10-15 16:33:59
                          [name] => Tea
                          [totalqty] => 3
                      )
                  [1] => stdClass Object
                      (
                          [product_id] => 2
                          [sale_datetime] => 2018-10-16 10:44:14
                          [name] => Tea
                          [totalqty] => 5
                      )
                 )
      )
  [1] => Illuminate\Support\Collection Object
      (
          [items:protected] => Array
              (
                  [0] => stdClass Object
                      (
                          [product_id] => 3
                          [sale_datetime] => 2018-11-15 18:04:36
                          [name] => Coffee
                          [totalqty] => 20
                      )
              )
      )
)

and i want to make array like below array

Array
(
  [0] => Illuminate\Support\Collection Object
      (
          [items:protected] => Array
              (
                  [0] => stdClass Object
                      (
                          [product_id] => 2
                          [sale_datetime] => 2018-10-15 16:33:59
                          [name] => Tea
                          [totalqty] => 3
                      )

                  [1] => stdClass Object
                      (
                          [product_id] => 2
                          [sale_datetime] => 2018-10-16 10:44:14
                          [name] => Tea
                          [totalqty] => 5
                      )
                  [2] => stdClass Object
                      (
                          [product_id] => 3
                          [sale_datetime] => 2018-11-15 18:04:36
                          [name] => Coffee
                          [totalqty] => 20
                      )
                 )
      )
)

via Chebli Mohamed