code: func (p *pathTree) add(rel string) {
  	if !p.caseSensitive {
  		rel = strings.ToLower(rel)
  	}
  	p.leafs.Add(rel)
  	parentDirs(rel, func(par string) bool {
  		p.nodes.Add(par)
  		return true
  	})
  }
docs: // add adds a native path 'rel', all its parents and all its children to the
  // path tree.