将list转化为treeData

```

export function tranListToTreeData(list, rootValue) {

  const arr = []

  list.forEach(item => {

    if (item.pid === rootValue) {

      const children = tranListToTreeData(list, item.id)

      if (children.length) {

        item.children = children

      }

      arr.push(item)

    }

  })

  return arr

}

```