Directory TreeView in Delphi FMX - delphi

Question

I made a directory TreeView in Delphi FMX, but when I expand 'C:\Windows\WinSxS' it contains 15000 folders. It took a lot of time, but it doesn't expand. On the other hand, when I tried to do it with a VCL TreeView, it worked fine, as it should. Is there any way to make it fast?
Here is my code:
function SlashSep(const Path, S: String): String;
begin
{$IF DEFINED(CLR)}
if Path[Length(Path)] <> '\' then
{$ELSE}
if AnsiLastChar(Path)^ <> '\' then
{$ENDIF}
Result := Path + '\' + S
else
Result := Path + S;
end;
procedure GetDir(const ParentDirectory: string; ParentItem: TTreeViewItem);
var
Status: Integer;
SearchRec: TSearchRec;
Node: TTreeViewItem;
begin
Status := FindFirst(SlashSep(ParentDirectory, '*.*'), faDirectory, SearchRec);
try
while Status = 0 do
begin
if (SearchRec.Attr and faDirectory = faDirectory) then
begin
if (SearchRec.Name <> '.') and (SearchRec.Name <> '..') then
begin
Node := AddChild(ParentItem,ExtractFileName(SearchRec.Name));
Node.HasChildren := True;
end;
end;
Status := FindNext(SearchRec);
end;
finally
FindClose(SearchRec);
end;
end;
procedure TForm1.ItemOnExpanding(Sender: TObject; Node: TTreeViewItem);
var
i: Integer;
begin
for i := Node.Count - 1 downto 0 do
TreeView1.RemoveObject(Node.Items[i]);
Node.BeginUpdate;
GetDir(GetPathItem(node),node);
Node.EndUpdate;
end;
It's expanding from here:
procedure TCustomTreeView.ItemExpanded(const Item: TTreeViewItem);
var
I: Integer;
Child: TTreeViewItem;
AllowExpansion: Boolean;
begin
InvalidateGlobalList;
if Item.IsExpanded then
for I := 0 to Item.Count - 1 do
begin
Child := Item.Items[I];
if not Child.IsInflated then
Child.Inflate;
end;
RealignContent;
//end;
if Assigned(FOnExpanding) then
if Item.IsExpanded then
FOnExpanding(Self, Item, AllowExpansion)
else
if Assigned(FOnCollapsing) then
if not Item.IsExpanded then
FOnCollapsing(Self, Item, AllowExpansion)
end;