As others have said, it takes time. I find it also fluctuates over time, i.e. sometimes I trust my T a lot, then again not for a few weeks.

It has always helped me to talk about the fact that I have difficulty trusting. For example just last session, in the beginning I told T that I felt like I couldn't trust him. We talked about that, and halfway into the session we got to a topic which I'd say requires lots of trust on my part. Just happened naturally.