json数据转换，如何将扁平化数组转为树形结构?

如何将扁平化的数组转成树形结构，比如： const a = [[1,2,3],['a','b','c'],['A','B','C']]; 要求a数组转化后结果，如：

[
  {
    label: '1',
    children: 
      [
        { label: 'a',
          children:[
            {
              label:'A'
            }
          ]
        }
      ]
  },
{
    label: '2',
    children: 
      [
        { label: 'b',
          children:[
            {
              label:'B'
            }
          ]
        }
      ]
  },
  {
    label: '3',
    children: 
      [
        { label: 'c',
          children:[
            {
              label:'C'
            }
          ]
        }
      ]
  },
]

实现代码

var a = [
    ['111', '222', '3333'],
    ['xxx', 'qqq', 'abcd'],
    ['xxx', 'qqq', 'abcd'],
    ['xxx', 'qqq', 'abcd'],
    ['xxx', 'qqq', 'abcd']
];

var res = [];
for (let i = 0; i < a[0].length; i += 1) {
  const obj = {}
let el = obj
for (let j = 0; j < a.length; j += 1) {
     if (j === 0 ) {
       el.label = a[j][i]
       el.children = []
     } else {
       el.children.push({
         label: a[j][i],
         children: []
       })
       el = el.children[0]
     }
  }
  res.push(obj)
}
console.log(res)