{
    "array": [{
            "parent_id": "A",
            "children": [{
                    "id": "a1"
                }, {
                    "id": "a2"
                }
            ]
        }, {
            "parent_id": "B",
            "children": [{
                    "id": "b1"
                }, {
                    "id": "b2"
                }
            ]
        }
    ],
}

[{"parent_id": "A", "id": "a1"}, {"parent_id": "A", "id": "a2"}...]