After you load your object you need to set the transparency for the object...
Try this ....
Load Object "media\mytree.x", 1
Set Object Transparency 1,4
The seond parameter is the transparency mode number, they are defnied as :
0 - draw first no alpha
1 - draw first with alpha masking
2 and 3 - draw second which overlaps solid geometry
4 - draw second alpha test (only render beyond 0x000000CF alpha values)
5 - water line object (seperates depth sort automatically)
6 - combination of 3 and 4 (second phase render with alpha blend AND alpha test, used for fading LOD leaves)
You can play with the mode but I suggest mode 4 or 6 to prevent "background bleeding" around the leaves.
Hope this helps