code: @SuppressWarnings("WeakerAccess")
      @UiThread
      public boolean popToRoot(@Nullable ControllerChangeHandler changeHandler) {
          ThreadUtils.ensureMainThread();
  
          if (backstack.size() > 1) {
              //noinspection ConstantConditions
              popToTransaction(backstack.root(), changeHandler);
              return true;
          } else {
              return false;
          }
      }
docs: Pops all {@link Controller} until only the root is left
  
  @param changeHandler The {@link ControllerChangeHandler} to handle this transaction
  @return Whether or not any {@link Controller}s were popped in order to get to the root transaction