In Violet City. Follow the path that's in between the house and the Market, go past the girl & Boy that are just standing there and you'll find it.
get your starting Pokemon to spray pokejizz on it
The wiggly tree is actually Sudowoodo. You need to get the badge in Goldenrod City. Then you go to the Flower Shop (next to the gym) and get squirtbottle. Use the squirtbottle on Sudowoodo and it will attack you. Defeat it or catch it and you will be able to get past.
you get the squirtbottle at the flower shop and water the tree(which is Sudowoodo)
You cannot remove the tree until you get to Goldenrod City (Go south from Violet City and make your way around). You can then get the watering can in Goldenrod City and use it on the tree.
beat the goldenrod gym then go to the flower shop in goldenrod and she'll give you the squirt bottle
go to goldenrod city get the squirtbottle spray it on the wiggly tree and you battle sudwoodo
Very specific! After you get to Goldenrod City, there's a Flower shop in the corner of town. The girl there will tell you that she'll give you a watering can after you beat the gym leader. Beat Whitney, and then return to the Flower Shop. The girl will give you a Squirtbottle, and you're free to return to Violet City to use it. Although I wouldn't recommend going all the way back through Ilex Forest, and the cave, just to get to Violet City to use the Squirtbottle. I believe if you go a little farther past Goldenrod, there will be a fork in the road where you can go to the Suduwoodo tree and use it. Then you can just walk past the area where the tree was at, and you'll be in Violet City territory.
You find it after you fight the wiggly tree.
put the controller down and get a life!
First defeat the tree that moves when you touch it (west of Violet City, north of Goldenrod) and go north.
To the west of violet city is the "odd tree" blocking your path. Talk to the fat Guy standing on the east side of the tree and he will give you rock smash.