If the tree on your island is close to the middle island
You can jump on it and brake the middle of the tree and place a block on it like wood, sand/stone or dirt (but first you have to get the block so go down and look in the 3 chests and get the sand/wood/dirt (if there is no dirt/wood/stone/ or wood brake a simple block on the tree then clime it up))
place 4 TNT all around you and you
HAVE good armor. if not, you die with the other players
place 2 TNT on top of the 4 TNTs you placed,
BUT place them in the opposite direction (so there will be more force on the back and not the font so that u will go front ward)
place a presser plate on the block you block on the middle of the tree. Then jump on it and stand in the
MIDDLE of all the TNTs and wait 4.5 secants (I think that's right; I'll test it)
and blast into the pool in the middle (its is hard to but with prates you can be as good as: Superla767 (he jumps this all the time)