after adding array1 using key1:
$VAR1 = {
          'key1' => [
                      [
                        'one',
                        'two',
                        'three'
                      ]
                    ]
        };

after adding array2 using key1:
$VAR1 = {
          'key1' => [
                      [
                        'one',
                        'two',
                        'three'
                      ],
                      [
                        'four',
                        'five',
                        'six'
                      ]
                    ]
        };

after adding array3 using eight:
$VAR1 = {
          'key1' => [
                      [
                        'one',
                        'two',
                        'three'
                      ],
                      [
                        'four',
                        'five',
                        'six'
                      ]
                    ],
          'eight' => [
                       [
                         'seven',
                         'eight',
                         'nine'
                       ]
                     ]
        };