The trees that need frost protection, but more light I have in a makeshift "greenhouse" on my from balcony, which gets a fair amount of light in winter and the trees that don't need light, but need temps to generally be above freezing, I have in a similar makeshift "greenhouse on my back balcony, which has stayed above freezing even though it has been close to -5 C these last few nights. Originally, I wanted to keep the top open of the back greenhouse, but I changed it.. as I saw that this winter would be pretty cold.
The first pic is the front "greenhouse" which is basically made around an Ikea shelving unit. The bubble-wrap goes all the way around the unit.
The second and third pics are the other "greehouse" the fourth was with the top open...