XPM to be used as Bitmaps or Images ?

I have an xpm (colour) and also xbm files (black and white) that I want
to use in my TK scripts where I would like to replace some default
bitmaps that are already existing by mine.

What do I have to do, I went through the documentation and found that I
have to use "image create" or "create image" but this is to create our
own stuff, I am looking for something that takes a X-11 bitmap format
file like .xpm file and convert it to a TCL/TK compatible bitmap or
photo file.

And then once this is done how can I use/source it ?

An example :

Tree $tree

$tree insert end root home <-image/-bitmap> "<filename>"

Thank you.
-C.

.