type
  PTreeData = ^TTreeData;
  TTreeData = record
    Column0: TDate;
    Column1: Integer;
    Column2: String;
  public
    function ToString(Index: Integer): string; inline;
  end;

implementation

{ TTreeData }

function TTreeData.ToString(Index: Integer): string;
begin
  case Index of
    0: Result := DateToStr(Self.Column0);
    1: Result := IntToStr(Self.Column1) + ' days';
    2: Result := Self.Column2;
  end;
end;

procedure TForm1.VirtualStringTreeGetText(Sender: TBaseVirtualTree; Node: PVirtualNode; Column: TColumnIndex; TextType: TVSTTextType;
  var CellText: string);
var
  Data: PTreeData;
begin
  Data := Sender.GetNodeData(Node);
  CellText := Data.ToString(Column);
end;