what size trees do you recommend to coincide with 1/35 scale?
also what size coincide with 1/48 scale?

trees come in many sizes so i think a small tree in 1/35 can work fine as a big tree in 1/48 unless the size of the leaves are a problem

Young trees that don't overwhelm the figures and vehicles are probably best for our purposes. An average, fully grown shade tree is often forty or fifty feet tall (between one and two feet in 1/35th scale). Even in smaller scales, full sized trees would still dwarf anything short of a railroad gun.
For fall and winter scenes, bare trees made from real tree roots can be very convincing, and don't overwhelm the model.
To calculate the size of anything in scale, just divide the original object's size by the denominator of the scale (35 for 1/35th, 48 for 1/48th).

Let the scene or idea dictate the size of the trees. Too small compared to your model, they will look toylike/silly ... too big they will drown and take over the scene. Experiment with what LOOKS RIGHT. Forget about scales and measurements. Take a look at nature, anything is possible ... so compose the tree to suit what you have in mind.

Actually no ... its nothing to do with being a rookie or an experienced modeller IMO. No point making things harder than what they are. If it looks right, for a tree it will be OK. All human beings know what a tree looks like and can judge the size of a leave. By "looking right" I mean eyeing the scale, not "its not normal but it will do". I think we can all make that judgement.

I look at it as a 1/35 figure is about 2-2.25 " tall and I assume that to be a 6ft tall man for general purposes. So a 6" +/_ tree is about 18 ft in 1/35 scale. Go from there on how it looks a fits in for you.
Do the same for a 1/48 figure-to-tree proportion.
Cheers!
Rick