JSFiddle - React, Tailwind, and code Playground

JavaScript

var ob = {
    name: "root",
    id: 1,
    children: [
        {
        name: "child one",
        id: 11,
        children: [
            {
            name: "grand child 1",
            id: 111,
            children: []},
        {
            name: "grand child 2",
            id: 112,
            children: []}
        ]},
    {
        name: "child two",
        id: 12,
        children: []}
    ]
};

function findObjectById(root, id) {
    if (root.children) {
        for (var k in root.children) {
            if (root.children[k].id == id) {
                return root.children[k];
            }
            else if (root.children.length) {
                return findObjectById(root.children[k], id);
            }
        }
    }
};

var bla = findObjectById(ob, 111);

console.log(bla);
bla.children.push({
        name: "child x",
        id: 1111,
        children: []
});
console.log(ob);