I live in an apartment and have no clue how strong the walls are. I bought pulleys and rope, then stopped - can do without a huge bill for a destroyed wall!
I use a 4x2 with 5/16" dowels (off-cuts from making arrows - I hate to waste stuff) every inch at a slight downward angle. I clamp it to my balcony door.
A good way to check symmetry is to take a flat on, as level as possible photo as you can then open in Photoshop and flip a layer copy with 50% transparency - shows up where things are out of whack.
If you don't have/can't justify the cost of Photoshop there's an open source (free) application that will do the trick - it's called GIMP
https://www.gimp.org/ Here's a photo of the tree
https://postimg.org/image/tofel31sb/ - text link in case image doesn't show up.