code: @SuppressWarnings("unchecked")
      private void expand()
      {
          try {
              final String key = getCacheKey();
              if (Context.getThreadContext().containsSessionAttribute(key)) {
                  final Set<UUID> sessMap = (Set<UUID>) Context
                                  .getThreadContext().getSessionAttribute(key);
                  setExpandedInternal(sessMap.contains(this.classificationUUID));
                  for (final UIClassification uiClazz : getDescendants()) {
                      if (sessMap.contains(uiClazz.classificationUUID)) {
                          uiClazz.setExpandedInternal(true);
                      }
                  }
              }
          } catch (final EFapsException e) {
              UIClassification.LOG.error("Error reading Session info for UICLassificagtion called by Filed with ID: {}",
                              this.fieldId, e);
          }
      }
docs: Expand the Tree.