Returns the receiver's parent item, which must be a
<code>TreeItem</code> or null when the receiver is a
root.
@return the receiver's parent item
@exception SWTException <ul>
<li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
<li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
</ul>
Returns the receiver's parent item, which must be a <code>TreeItem</code> or null when the receiver is a root.
@return the receiver's parent item
@exception SWTException <ul> <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li> <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li> </ul>