มีท่านใดเคย นำ function เรียกใช้ตัวเองมาใช้ประโยชน์ บ้างครับ ช่วย แสดงความคิดหน่อย

<script type="text/javascript">

var gData = [
    {id:1,name:'A',parent_id:0},
    {id:2,name:'B',parent_id:7},
    {id:3,name:'C',parent_id:1},
    {id:4,name:'D',parent_id:10},
    {id:5,name:'E',parent_id:8},
    {id:6,name:'F',parent_id:0},
    {id:7,name:'G',parent_id:10},
    {id:8,name:'H',parent_id:1},
    {id:9,name:'I',parent_id:6},
    {id:10,name:'J',parent_id:0},
    {id:11,name:'K',parent_id:6},
    {id:12,name:'L',parent_id:9},
    {id:13,name:'M',parent_id:9},
];

function fetchByParentId(parent_id){
    var fake = 'SELECT * FROM tb WHERE parent_id="'+parent_id+'"';    
    var a=[];
    for(var i in gData){
        if (gData[i].parent_id==parent_id){            
            a.push(gData[i]);
        }
    }
    return a;
}


function renderTree(id){
    var children = fetchByParentId(id);    
    if (children.length){
        document.write('<ul>');
    }
    for(var i in children){
        document.write('<li>');
        document.write(children[i].name);
        renderTree(children[i].id);
        document.write('</li>');
    }
    if (children.length){
        document.write('</ul>');
    }    
}

renderTree(0);

</script>