When discussing the character of Adam, Matt really wanted him to feel like a guy that you would meet in “everyday life.” He said:
“What’s always struck me about those in that line of work is how brilliantly they fit into everyday life — how well and easy it would be to meet them at a party or sit next to them on the tube, have a little chat with them and not know what they do for a living. These are people who aren’t just good at pretending to be part of us, they are part of us. They’re drawn from our world and our society… I wanted Adam to feel that way… He had to feel real and relatable and fallible, and that was my starting point for him… I wanted this to feel like we could imagine this guy going to work, we could imagine what he was doing and the toll it takes on him, then he comes home and he has to have dinner with his kids and not tell them a thing. That’s real and it happens to people.”
Source: https://www.distractify.com/p/is-treason-based-on-a-true-story
