One dimensional array to tree array

let arr = [{
    id: 1.pid: 0.title: 'home'
}, {
    id: 2.pid: 1.title: 'Order List'
}, {
    id: 3.pid: 1.title: 'Post Management'
}, {
    id: 4.pid: 3.title: 'Post list'
}, {
    id: 5.pid: 3.title: 'Post Settings'
}, {
    id: 6.pid: 0.title: 'login'
}];
let map;

function arrToMap(arr) {
    map = new Map(a);for (let index in arr) {
        const item = arr[index];
        item.children = [];
        map.set(item.id, item)
    };

    const res = arr.filter(item= > item.pid === 0);
    for (let index in arr) {
        const item = arr[index];
        if (item.pid === 0) continue;
        const parent = map.get(item.pid);
        parent.children.push(item);
        item.parent = parent;
    }
    return res;
};

console.log(arrToMap(arr))
// Get the corresponding data according to the id
function getTitle(id) {
    let list = [];
    let items = map.get(id);
    while (items) {
        list.unshift(items.title);
        items = items.parent;
    }
    return list;
}

console.log(getTitle(5))
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