Well to get past the tree it has to be at night on a windy day, always forget that part. And to get into the cave generally most people on here have used Wednesday set at 2:47 am. If that doesn't work just keep changing the date/week until the tree disappears. I, myself have to work my way back to this point and get my impish natured Leafeon back.
About the cave to the left of spinel town, not Tarzan mountain all it holds is a mystic water and gastradon are common there. Which is a good training ground of pokemon like Lilligant and Accelgor. To get access from what I can remember you just have to circle around the maze in Chrysolia Forest until the tree disappears.