procedure TForm1.TreeView1Click(Sender: TObject); 
var 
  aPoint: TPoint; 
  aNode: TTreeNode; 
  aHitTest: THitTests; 
begin 
  if GetCursorPos(aPoint) then 
  begin 
    aPoint := TreeView1.ScreenToClient(aPoint); 
    aHitTest := TreeView1.GetHitTestInfoAt(aPoint.X, aPoint.Y);

    //htOnItem, htOnButton, htOnIcon, htOnIndent, htOnLabel 
    if not ((htOnItem in aHitTest)or (htOnLabel in aHitTest)) then  Exit;

    aNode := TreeView1.GetNodeAt(aPoint.X, aPoint.Y); 
    if not Assigned(aNode) then  Exit;

    //test: Caption := aNode.Text; 
    //do your code 
  end; 
end;

procedure TForm1.TreeView1MouseDown(Sender: TObject; Button: TMouseButton; 
  Shift: TShiftState; X, Y: Integer); 
var 
  aNode: TTreeNode; 
begin 
  aNode := TreeView1.GetNodeAt(X, Y); 
  if not Assigned(aNode) then  Exit;

  //do your code 
end;