Recursive Function on Ruby on Rails

I have a mysql table that I am tracking relating items. (this table belong to Artilce table) [this is the datastructer from mysql][1] [1]: https://ift.tt/YDls7aO

how can I generate a json from Ruby that looks like this. (I need that for D3JS visualisation tree)

{
"id":1,
"art_type":"V",
"children":[
{
    "id":7,
    "art_type":"V",
    "children":[
        {
            "id":9,
            "art_type":"V",

        },
        {
            "id":10,
            "art_type":"V",
        }
    ]
},
{
    "id":8,
    "art_type":"V",
    "children":[
        {
            "id":11,
            "art_type":"R"
        },
        {
            "id":12,
            "art_type":"V"
        },
        {
            "id":13,
            "art_type":"V"
        }
    ]
}
]

}