var chapterTree = {
  name: '总章节',
  children: [
    {
      name: '章节一',
      children: [
        {
          name: '第一节', 
          children: [
            {name: '第一小节'},
            {name: '第二小节'}
          ]
        },
        {name: '第二节'}
      ]
    },
    {
      name: '章节二',
      children: [
        {name: '章节2-1'},
        {name: '章节2-2'}
      ]
    }
  ]
}

function addLabel(tree){
  // TODO
}

const result = addLabel(chapterTree)
console.log(result); // ["总章节", "(1)章节一", "(1.1)第一节", "(1.1.1)第一小节", "(1.1.2)第二小节", "(1.2)第二节", "(2)章节二", "(2.1)章节2-1", "(2.2)章节2-2"]