JSFiddle - React, Tailwind, and code Playground

JavaScript

var employees= [
  {name:"Jeff",manager:null,title:"The Pres"},
  {name:"Amy",manager:"Aaron",title:"lll"},
  {name:"Chris",manager:"Aaron",title:"lll"},
  {name:"Dana",manager:"Aaron",title:"lll"},
  {name:"Joe",manager:"Aaron",title:"lll"},
  {name:"Mike",manager:"Aaron",title:"lll"},
  {name:"Aaron",manager:"Jeff",title:"lll"}
];

var hash = {};
var root;

for (var i = 0; i < employees.length; i++) {
    var employee = employees[i];
    hash[employee.name] = {
        name:employee.name, manager:employee.manager, title:employee.title, children: []
    };
}
for (var i = 0; i < employees.length; i++) {
    var employee = hash[employees[i].name];
    var manager = hash[employee.manager];
    if (manager) {
        manager.children.push(employee);
    } else {
        root = employee;
    }
}

console.log(root);