Most, if not all, of new wood put in an aquarium will get this whitish looking gelatinous fungi growing on it. Sure, it looks unsightly, but it is harmless, and in time it will retreat.
Some fish, especially plecos, will thank you because they love to eat it. Some hobbyists go to the painstaking trouble of periodically taking the wood out and scrubbing it until a time when it grows no longer.
It's plausible that it's down to remnants of sugars from the sap of the tree which this particular whitish fungus likes. Once the fungus has used up this food source then that is when it stops growing.