Create recrursive tree from relational data source

recursive-tree.js

let d = [{
  "name": "CEO",
  "parent": null,
  "id": "5847e80312896b2fa49ce428"
}, {
  "name": "A",
  "parent": "5847e80312896b2fa49ce428",
  "id": "5847f58289046550aa05a49d"
}, {
  "name": "A1",
  "parent": "5847f58289046550aa05a49d",
  "id": "584804b073697edd3d372529"
}, {
  "name": "A2",
  "parent": "5847e80312896b2fa49ce428",
  "id": "584804b073697edd3d372539"
}]

const rec = (parent, arr) => {
  const ref = parent ? parent.id : null
  const children = arr.reduce((ac, x) => {
    if (x.parent === ref)
      ac.push(rec(x, arr))
    return ac
  }, [])
  if (parent)
    parent.children = children
  return (
    parent ?
    parent :
    children[0]
  )
}

const res = rec(null, d)

console.log(res)