Relationship between id and pid in ztree?

Question

I'm new to ztree Jquery plugin.Kindly somebody help me to understand the relationship between id and pid with the below code.

var zNodes =[
    {id:1, pId:0, name:"[core] Basic Functions", open:true},
    {id:101, pId:1, name:"Standard JSON Data"},
    {id:102, pId:1, name:"Simple JSON Data"},
    {id:103, pId:1, name:"Don't Show Line"},
    {id:104, pId:1, name:"Don't Show Icon"},
    {id:105, pId:1, name:"Custom Icon - icon"},
    {id:106, pId:1, name:"Custom Icon - iconSkin"},
    {id:107, pId:1, name:"Custom Fonts"},

    {id:2, pId:0, name:"[excheck] Checkbox & Radio", open:false},
    {id:201, pId:2, name:"Checkbox Operation"},
    {id:202, pId:2, name:"Checkbox nocheck Demo"},
    {id:203, pId:2, name:"Checkbox chkDisabled Demo"}
    ]

Thanks in advance.