code: func (v *TreeVertex) Find(id string) *TreeVertex {
  	if v.Id == id {
  		return v
  	}
  	for _, u := range v.Descendants {
  		if r := u.Find(id); r != nil {
  			return r
  		}
  	}
  	return nil
  }
docs: // Find searches for a vertex who's id is the given id.
  // Returns the first vertex it finds with such an Id, or nil if not found