@Override
protected void execInitField() throws ProcessingException {
  //Fetch the LookupRows:
  SomeLookupCall call = new SomeLookupCall();
  List<? extends ILookupRow<Long>> lookupRows = call.getDataByAll();

  //Build the Tree:
  ITree tree = getTree();
  tree.removeAllChildNodes(tree.getRootNode());

  P_TreeNodeBuilder builder = new P_TreeNodeBuilder();
  List<ITreeNode> children = builder.createTreeNodes(lookupRows, ITreeNode.STATUS_NON_CHANGED, true);
  tree.addChildNodes(tree.getRootNode(), children);
  tree.selectFirstNode();
  tree.expandAll(tree.getRootNode());
}

public void refreshTree() throws ProcessingException {
  //Selection Key:
  Object key = null;
  if (getTree().getSelectedNode() != null) {
    key = getTree().getSelectedNode().getPrimaryKey();
  }

  //Fetch the LookupRows:
  SomeLookupCall call = new SomeLookupCall();
  List<? extends ILookupRow<Long>> lookupRows = call.getDataByAll();

  //Build the Tree:
  ITree tree = new Tree();
  setTree(tree, false);
  tree.removeAllChildNodes(tree.getRootNode());

  P_TreeNodeBuilder builder = new P_TreeNodeBuilder();
  List<ITreeNode> children = builder.createTreeNodes(lookupRows, ITreeNode.STATUS_NON_CHANGED, true);
  tree.addChildNodes(tree.getRootNode(), children);
  tree.selectNode(tree.findNode(key));
  tree.expandAll(tree.getRootNode());
}