there is a database as follows:

< table > < thead > < tr > < th > id < / th > < th > pid < / th > < th > name < / th > < / tr > < / thead > < tbody > < tr > < td > 1 < / td > < td > 0 < / td > < td > a < / td > < / tr > < tr > < td > 2 < / td > < td > 1 < / td > < td > b < / td > < / tr > < tr > < td > 3 < / td > < td > 2 < / td > < td > c < / td > < / tr > < tr > < td > 4 < / td > < td > 2 < / td > < td > d < / td > < / tr > < tr > < td > 5 < / td > < td > 1 < / td > < td > e < / td > < / tr > < tr > < td > 6 < / td > < td > 2 < / td > < td > f < / td > < / tr > < tr > < td > 7 < / td > < td > 5 < / td > < td > g < / td > < / tr > < tr > < td > 8 < / td > < td > 5 < / td > < td > h < / td > < / tr > < tr > < td >. < / td > < td >. < / td > < td >. < / td > < / tr > < / tbody > < / table >

pid: represents parent ID

get this data and how to code the tree result (json format) back to the front end.

{
    "id": 1,
    "name": "a",
    "children": [
        {
            "id": 2,
            "name: "b",
            "children": [
                {
                    "id": 3,
                    "name": "c",
                    "children": [ ... ] // 
                },
                {...},
                {...},
            ]
        },
        {
            "id": 5,
            "name": "e",
            "children": [
                {
                    "id": 7,
                    "name": "g"
                },
                {
                    "id": 8,
                    "name": "h"
                }
            ]
        },
    ]
}

there is no limit to the number of sons down, and there is only one node at the top.