Angular CanActivate guard - createUrlTree relative navigation

I currently have a route guard such as

export class EntityGuard implements CanActivate {
  constructor(private readonly router: Router, ...) {}

  canActivate(
    route: ActivatedRouteSnapshot,
    state: RouterStateSnapshot
  ): Observable<boolean | UrlTree> {

  ...

This guard is activated for the URL

basePath/select/10/123

which means

basePath/select/:type/:id

When a certain condition is met, I need to force navigation back to

basePath/select/:type

How can I do that using createUrlTree? E.g.

if (...) {
   return of(this.router.createUrlTree([../', type]));
}

I'd need to set the

{ relativeTo: parent }

option. However I can't seem to find a way to do it.

My current solution is

private navigateBack(route: ActivatedRouteSnapshot, state: RouterStateSnapshot) {
  const end = state.url.indexOf(route.url[route.url.length - 1].path);
  const parentUrl = state.url.slice(0, end);
  return of(this.router.createUrlTree([parentUrl]));
}

Which I really don't like. String manipulation is big no for me.