Store an array of JSON data in mysql database

 $arr = [
            'organization_id' => $organization_id,
            'user_id' => $user_id
        ];
        $data = json_encode($arr);

With above code I am able to insert data as

{"organization_id":1,"user_id":1}

But, next time I run the same function (with different organization and user id value), I want to store this data as follow:

[{"organization_id":1,"user_id":1}, {"organization_id":2,"user_id":5}]

How can I achieve this.