We have an enormous oleander tree (at least I consider it to be enormous). It's over 12 feet tall and 10 feet in diameter. The previous owner had pruned it to look like a ball suspended on its branches, and it looked great when we first moved it. Now it is just overwhelmingly large, and is crowding out another oleander and a bottle brush nearby.

I went out to cut this thing down to size, but when I did a test cut of less than 2 feet of green growth, I saw that if I tried to do this to the entire tree, it would basically look like a big ball of bare twigs - that is, there are no green leaves deeper inside this behemoth. There are also very thick branches that would be exposed if I cut it back so drastically.

What should I do about this? I know that these "shrubs" are virtually indestructible, but I'm worried that if I cut it down too severely, it would not recover quickly and would be an eyesore for some time. Do I need to consult an arborist about what to do?