+Gets the specified item image. The value of {\it which} may be:
+
+\begin{itemize}\itemsep=0pt
+\item{wxTreeItemIcon\_Normal} to get the normal item image
+\item{wxTreeItemIcon\_Selected} to get the selected item image (i.e. the image
+which is shown when the item is currently selected)
+\item{wxTreeItemIcon\_Expanded} to get the expanded image (this only
+makes sense for items which have children - then this image is shown when the
+item is expanded and the normal image is shown when it is collapsed)
+\item{wxTreeItemIcon\_SelectedExpanded} to get the selected expanded image
+(which is shown when an expanded item is currently selected)
+\end{itemize}