I have been looking through all the types of saplings, and can't find out what sapling will get me mahogany wood. I am guessing it is a tree breeding, buildcraft, addon.
Mahogany Saplings will get you Mahogany Wood. And it is from tree breeding, more specifically from Forestry. Sir Sengir is rather vague on the subject but there's a spoiler guide floating around here within the first few pages of this subforum that has most of the tree combinations.
Yea, I saw that there wasn't a mahogany sapling and was trying to find out the sapling that did get you it. There were 6 or 7 saplings that I didn't check because bone meal didn't affect it.