Sorry, I don't understand the "leaf colossus" northwest tree to reach the Unown. I tried clicking the tree in that screen. What do I do?
Did you get the rare orb (key item) ? If no, you can obtain it by talking to a guy in a house (on a road I believe), I've read that you also might bring a psychic type pokemon in your party. After that when clicking the top-left corner tree in the Ruins of Alph, you should be able to access the zone at the bottom of the screen.