isInclude (parent, target) {
    const children = parent.children
    if (children.length === 0) {
      return false
    } else {
      if (children.some(child => child.key === target.key)) {
        return true
      } else {
        return children.some(child => this.isInclude(child, target))
      }
    }
  }
if target is descendant of parent return true, else return false
@param  {[type]}  parent [description]
@param  {[type]}  target [description]
@return {Boolean}        [description]