Trees have no impact on cell service.
I live on what you would call a plateau / cliff (approx. 250 - 300 Ft. +/- above the valley I overlook.
Yet if I jump in a car and move / go to a property (on the private road, while staying in my car) that has a clear view (they clear cut their 5 acre plot) from the road to the cliff / view, I get a GREAT signal. Both the T-Mobile LG Flip phone & the Samsung S9.
My daughter just brought me a new Samsung S9, I get approx. 1 (one) bar. My previous cell phone was a flip phone ZERO bars. I think that also played a part, i.e. old technology. Depending where I decide in my house to try and make a call on the new Samsung S9 Verizon, still not able to make a call.
That's my story, I'm sticking to it.
Bull.
Trees will affect cell service.
And satellite radio.
And radar.
And GPS.
And.....
Varying levels. But Never say Never.
Old fart with fifty plus years RF experience, 1MHz to 30GHz.