Generate tree from flat pages

tree.js

var pages = [
    {id: 1, parent: null, name: 'First'},
    {id: 2, parent: null, name: 'Second'},
    {id: 3, parent: 2, name: 'First child of second'},
    {id: 4, parent: 2, name: 'Second child of second'},
    {id: 5, parent: 2},
    {id: 6, parent: 4},
    {id: 7, parent: 4},
    {id: 8, parent: 6}
];

console.log('here is the tree', generateTree(pages));

function generateTree (pages) {
    var map = {}, tree = [];
    
    function addChildrenToPage (page) {
        page.children = map[page.id] || [];
        for (var i = 0; i < page.children.length; i++) {
           addChildrenToPage(page.children[i], map);   
        }
    };
    
    for (page of pages) {
        if (!map[page.parent]) map[page.parent] = [page];
        else map[page.parent].push(page);
    }
         
    for (page of pages) {
        if (page.parent == null) {
              addChildrenToPage(page);
              tree.push(page);
        }
    }
    
    return tree;
};