The Ginso Tree is the 5th "level" that you will play through and the chronological order of the levels is as follows:
Moon GrottoGinso Tree
**There is also a video guide at the very end.**
Once you've received the Water Vein from Gumo within the Moon Grotto, you should use the Spirit Well to teleport to Thornfelt Forest and then enter the Ginso Tree. Jump through the portal on the right to exit from the left portal. Then jump up to the higher right portal to exit the higher left portal. Go through one more portal up and to the left to enter the next area.
Both the right and left walls are covered with portals with each portal sending you to the corresponding height on the other side. Make your way up to the top right portal to exit through the top left portal. From there, go through one more portal to exit the area. Bounce pad up through the next portal then clear the baddies to make it to the next one. Bounce pad up again but check out the small room through the right portal for a crystal before exiting through the top left portal.
Now you'll come to a bunch of portals that you have to "fall" to among the thorns. Be sure to time your jumps well and then exit the area in the top left one. Fall into the bottom right portal to emerge from the middle and push the log to the right to catch the fireball. Jump to the top left for a 2nd log and push this down as well and through the bottom left portal. The fireball should pass through each log and destroy the barrier to the top left allowing you to go to the next area, grabbing the crystal between the next two portals.
You'll get locked in with a worm mini boss creature that, once defeated, will open the other door. In the next area, drop down into the portal to reach the ledge in the middle. To the right are two keystones you must reach by falling and jumping between those two portals. Go through the top left portal of this room to enter the area with the other two keystones.
Fall through the portal in the bottom left to drop from the top and onto the brittle log to reach one keystone. Quickly jump off the 2nd brittle log and bounce pad up to the portal. Again, quickly grab the other keystone and jump off the brittle log through the portal and open the keystone door in the top right of the room to exit to the next area.
You will now unlock the Bash ability! Use this new ability on the lantern to the left to go through the portal in the top left. Keep bashing with lanterns and enemies to make your way over the first set of fireballs. On the second set, bash down off of a fireball and it will launch that fireball up into the brittle log letting you continue. Shoot the next fireball through the left portal breaking another log.
Proceed upwards until you see another worm shooting projectiles. Use these to make your way further up. You can break a log with one of these on the left which leads to a portal and an Energy Cell. Next, continue up for a keystone near some lanterns then go through the nearby portal for the 2nd keystone. Go up for the 3rd, left for the 4th and then up and left for the keystone door.
Through the portal is a floating-rock-orb mini boss that must be defeated using bash to launch back the projectiles. Be mindful of where you will land once you launch these. Once he's defeated, unlock the Spirit Well through the door on the right. Launch yourself up the lantern where the mini boss was to find the heart of the Ginso Tree, covered in corrupting spikes.
Your goal now is to clear these spikes and you will do so in two stages. Go into the left room and make your way to the top left where a spider launches projectiles. Fire these to the right to break the log. Go through the new opening and attack the corruption which will break and the clear the entire left side of the heart. Drop down and go through the right room.
This room requires a little more timing. Launch the fireball from the bottom right up to the hanging log. Beat it to the next log on the left and launch it up again. Do this for two more logs and it will smash the blockage in the top left of this area. Proceed through and attack the corruption again, freeing the heart and restoring the Element of Water. Now it's time to escape.
**As mentioned before, if you would prefer a video guide you can use this one by Gamer Walkthroughs:**