Answer: The black oak
In Korean, the "black oak" is called 참나무. The reason I say the black oak tree never lies is that one meaning for 참 is "truth," so 참나무 could literally be translated as the "truth tree," although I do not know if that is where the name came from. Here is a picture of a 참나무.
In an earlier post, here, I talked about "The Tree Song," which also mentions 참나무. Here is the line from the song:
I am not sure of the meaning of 대끼놈, but I have seen it used to refer to mischievous children. If anyone knows the exact meaning, I would appreciate it if you would let me know.