After getting the key to the Antenna Tree from the blob monster guy in Kelina Village, you can take the tree to Alice, a city by the sea.
ALICE
Going south after you go through the Antenna Tree, you will arrive in the city of Alice. To the south of Alice is the Bamu Sea, but many of the water monsters are angry with humankind.
Right after you get into Alice, go west and you will see a blue monster who calls himself Jinxi. He tells you not to talk to him, but you will need him later. If you go east out of Alice there is a forest path but you're not allowed to enter. If you go toward the Bamu Sea you will find a little monster who talks to you. He wants a game machine. If you didn't get one yet, you'll have to walk all the way back to Tulunk Village. There is a game machine that looks like a Gameboy in the Tulunk Village store. Buy that and take it back to the monster. He will then give you his phone number and allow you to swim. This lets you go through most water areas, including the Bamu Sea.
The Bamu Sea is a bit maze-like, but not too hard to navigate. You don't have to fight all the monsters in the sea but you can if you want extra experience. Going through the sea, you will find out that there is an Antenna Tree on a small island, but again you can't get into it because of a locked door. What you need to do is go as far west as you can in the Bamu Sea. There will be a pink octopus monster who you must talk to. He gives you some passwords. Take them back up to Alice and find the house that asks you to speak a password to gain entrance.
Once you do, there will be another octopus monster who allows you to warp to a small sea cave. Go inside and press the button. This will open up the Antenna Tree for you. Navigate through Bamu Sea again and go up to the tree, but then you will be challenged by a guy named Boundary who says he wants to destroy Antenna Trees. He has a monster called Anjiosi, which is a Sky type and will be good against Kuribute. You might want to switch your main monster to a Hill type. In the Speed version (Pokemon Jade), Boundary will have the monster Jimunosi, which is a Hill type. Fanges, the starting monster of the Speed version, should be good against him.
After defeating Boundary you can go through the Antenna Tree to your next destination.