I Want a More Concice Form of Data than an Array

Instead of going for a complex nested array, I decided that it might be best to keep it to simple two level set of arrays.

    $x = array(
            101 => [ (int $parent_id), (bool $completed)  ], 
            102 => [ (int $parent_id), (bool $completed)  ], 
            103 => [ (int $parent_id), (bool $completed)  ], 
            104 => [ (int $parent_id), (bool $completed)  ], 
            ...
        );

I realized that I was looking for something simpler like what python offers with its “list” data type. I feel like this is about as simple as I could get with storing an unorder list in PHP/MySQL. Anyone got anything better?