Retaining wall on a 2-way slope under an existing block wall
What's behind the wooden fence, your back yard?  Does the slope get even taller back there?  Would you dig out that slope and continue the retaining wall there?  You can reasonably build a retaining wall 3-4 feet high without major engineering but when you get to 6-8 feet high it has to retain much more weight (8x as much according to This Old House) and takes more engineering.  This may be more than you want to get into.

As Alaska man asked, is the tree next to the sidewalk yours, or is it the city's?  What do you plan to do with the brick wall?  It would need to be supported or removed also.  Would removing the tree or brick wall require city permits or an engineering study?  This may also be more trouble than it's worth.

With palm trees and bare dry dirt, I'm guessing you're in a dry area in the south western United States.  I'm in the central U.S., where we have thunderstorms 8-10 months out of the year.  A good thunderstorm or two would wash that loose dirt slope down against the house and risk toppling the brick wall so I would leave the slope as-is and sod it or put in low ground cover to hold the soil in place.  If I used grass I would then have to mow it.  I prefer a smooth slope I can just push a lawn mower up, rather than have to pull out a string trimmer for a few square feet of grass on top of a retaining wall.  For long-term durability and ease of maintenance, I'd recommend just adding sod or ground cover and leave the slope alone.