How to save/load to/from file in virtualtree component using Delphi?

I have downloaded the virtualtree component and the manual"Virtual TreeView tutorial". I follow the tutorial and coding step by step. Most of the function in tutorial is fine except the savetofile and loadfromfile do not work.

My node data is

type
  PMytreedata = ^TMYTreeData;
  TMYTreeData = record
    Column0: String;
    Column1: String;
    Column2: String;
  end;

The question is something string lose in column0,column1/2 when load from file.

The code is below

Create new node and data:

procedure TForm3.Button1Click(Sender: TObject); //CRETAE NEW NODE AND DATA
begin
  Randomize;
  Rand := Random(99);
  XNode := VST.AddChild(nil);

  if VST.AbsoluteIndex(XNode) > -1 then
  begin
    Data := VST.GetNodeData(Xnode);
    Data^.Column0 := IntToStr(Rand)+EDIT1.Text + 'One' ;
    Data^.Column1 := EDIT1.Text+'Two' + IntToStr(Rand + 10);
    Data^.Column2 := EDIT1.Text+'Three' + IntToStr(Rand - 10);
  end;
end;

procedure TForm3.Button2Click(Sender: TObject);//ADDCHILD
var
  XNode: PVirtualNode;
  Data: PMytreedata;
begin
  if not Assigned(VST.FocusedNode) then
     Exit;

   XNode := VST.AddChild(VST.FocusedNode);
   Data := VST.GetNodeData(Xnode);

   Data^.Column0 := EDIT1.Text ;
   Data^.Column1 := EDIT2.Text ;
   Data^.Column2 := EDIT3.Text ;

   VST.Expanded[VST.FocusedNode] := True;
end;

Save to file and load from file

procedure TForm3.Button4Click(Sender: TObject);
begin
    VST.SaveToFile('C:\vst.at1');
end;

procedure TForm3.Button5Click(Sender: TObject);
begin
    VST.LoadFromFile('C:\vst.at1');
end;

Get the node size without the code error

procedure TForm3.VSTGetNodeDataSize(Sender: TBaseVirtualTree;
  var NodeDataSize: Integer);
begin
    NodeDataSize := SizeOf(TMYTreeData);//WITHOUT THE CODE,ERROR COMING .
end;

Show text

procedure TForm3.VSTGetText(Sender: TBaseVirtualTree; Node: PVirtualNode;
  Column: TColumnIndex; TextType: TVSTTextType; var CellText: string);
var
  Data: PMytreedata;
begin
  Data := VST.GetNodeData(Node);
  case Column of
    0: CellText := Data^.Column0;
    1: CellText := Data^.Column1;
    2: CellText := Data^.Column2;
  end;
end;

LOAD FORM FILE

procedure TForm3.VSTLoadNode(Sender: TBaseVirtualTree; Node: PVirtualNode;
  Stream: TStream);//LOAD FORM FILE
var
  Data: PMytreedata;
  Len: Integer;
begin
      Data := VST.GetNodeData(Node);

      Stream.read(Len, SizeOf(Len));
      SetLength(Data^.Column0, Len);
      Stream.read(PChar(Data^.Column0)^, Len);

      Stream.read(Len, SizeOf(Len));
      SetLength(Data^.Column1, Len);
      Stream.read(PChar(Data^.Column1)^, Len);

      Stream.read(Len, SizeOf(Len));
      SetLength(Data^.Column2, Len);
      Stream.read(PChar(Data^.Column2)^, Len);
end;

SAVE TO FILE

procedure TForm3.VSTSaveNode(Sender: TBaseVirtualTree; Node: PVirtualNode;
  Stream: TStream); //SAVE TO FILE
var
  Data: PMytreedata;
  Len: Integer;
begin
  Data := VST.GetNodeData(Node);

  Len := Length(Data^.Column0);
  Stream.write(Len, SizeOf(Len));
  Stream.write(PChar(Data^.Column0)^, Len);

  Len := Length(Data^.Column1);
  Stream.write(Len, SizeOf(Len));
  Stream.write(PChar(Data^.Column1)^, Len);

  Len := Length(Data^.Column2);
  Stream.write(Len, SizeOf(Len));
  Stream.write(PChar(Data^.Column2)^, Len);
end;