private
    { Private-Deklarationen }
    FExpandNode,
    FCollapseNode : TTreeNode;



procedure TForm1.TreeView1DblClick(Sender: TObject);
begin
  FCollapseNode:=nil;
  FExpandNode:=nil;
end;

procedure TForm1.TreeView1MouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
var
  lExpandingEvent : TTVExpandingEvent;
  lCollapsingEvent : TTVCollapsingEvent;
begin
  if Assigned(FExpandNode) then
  begin
    lExpandingEvent:=TreeView1.OnExpanding;
    TreeView1.OnExpanding:=nil;
    FExpandNode.Expand(False);
    TreeView1.OnExpanding:=lExpandingEvent;
    FExpandNode:=nil;
  end;
  if Assigned(FCollapseNode) then
  begin
    lCollapsingEvent:=TreeView1.OnCollapsing;
    TreeView1.OnCollapsing:=nil;
    FCollapseNode.Collapse(False);
    TreeView1.OnCollapsing:=lCollapsingEvent;
    FCollapseNode:=nil;
  end;
end;

procedure TForm1.TreeView1Collapsing(Sender: TObject; Node: TTreeNode;
  var AllowCollapse: Boolean);
begin
  AllowCollapse:=False;
  FCollapseNode:=Node;
end;

procedure TForm1.TreeView1Expanding(Sender: TObject; Node: TTreeNode;
  var AllowExpansion: Boolean);
begin
  AllowExpansion:=False;
  FExpandNode:=Node;
end;