[wxPython] wxImage - Creating A New Image

I am creating an app which houses a wxTreeCtrl where I would like to place
images next to the various tree structure items. I have done this by using
wxImage.

If I wanted to use another image that is not part of wxImage, how would I
append the already included images ??

For example, I have a file called 'folder.gif' which I want to place on the
tree structure - would this be done using wxImage ??

Pete