Would be wise to boil any wood that you place in the aquarium for one cannot know where the wood originated from and what toxins,pollutant's,may have soaked into the wood if gathered from streams,rivers.Should also note that some tree's conatain sap which I would expect to be difficult to remove completely and could leach from the wood into the aquarium and gum up filters,or perhaps affect fish negatively.
With that said,,I have collected wood from along reasonably clean streams and lakes and after soaking it for a few weeks,and then boiling it,,Placed it in my aquariums and thus far(knocks wood) have seen no ill effects.
Probably safer to purchase wood which may have already been pressure washed ,rinsed,or gathered from area's where pollutant's are perhaps not a concern, but who knows for sure,where the wood offered for use in aquariums is gathered from?