Empty Space in Dialog Box

[Kamalpreet Grewal <grewalkamal005 gmail com>]

I am developing a dialog box. I have added a treeview and two buttons in it.

Adding the treeview to the scrolled window using:
_mainBox.pack_start(_scrolledWindow, Gtk::PACK_EXPAND_WIDGET);
where _mainBox is a Gtk::VBox.

The problem is I am getting empty space above the treeview. Why is it
so? As per the packing option used, the treeview should expand to fill
the widget space available to it.

Please help me fix this issue.

-- 
Kamalpreet Kaur Grewal
Blog: http://kamalpreetgrewal.com/