arr to tree：双层filter

function toTree(arr){

    let copyArr = JSON.parse(JSON.stringify(arr))  //深拷贝源数据

    return copyArr.filter(parent=>{

        let children = copyArr.filter(child=> child.parentId===parent.id)

        parent.children = children.length>0 ? children :  []

        return parent.parentId == null //返回顶层，依据实际情况判断这里的返回值

    })

}

console.log(toTree(arr))

---

let arr= [

　　{ id:0, parentId:null, name:"顶级菜单" },

　　{ id:1,  parentId:0, name:"一级菜单A" },

　　{ id:2, parentId:0, name:"一级菜单B"},

　　{ id:3, parentId:0, name:"一级菜单C"},

　　{ id:4, parentId:1, name:"二级菜单A-A"},

　　{ id:5, parentId:1, name:"二级菜单A-B"},

　　{ id:6, parentId:2, name:"二级菜单B-A"},

　　{ id:7, parentId:4, name:"三级菜单A-A-A"},

　　{ id:8, parentId:7, name:"四级菜单A-A-A-A"},

　　{ id:9, parentId:8, name:"五级菜单A-A-A-A-A"},

];