{ .... }
uses CommCtrl;
{ .... }
procedure SetTreeViewItemHeight(aTreeView: TTreeView; aItemHeight: Word);
begin
aTreeView.Perform(TVM_SETITEMHEIGHT, aItemHeight, 0);
end;
// Example:
procedure TForm1.Button1Click(Sender: TObject);
begin
SetTreeViewItemHeight(TreeView1, 30);
end;