I too can relate to a number of experiences in my early years that lead me down the path to crossdressing. So on the surface I would probably say for me it is nature.
But my Mom had told me that her doctor said she was having a girl. This was long before the days of testing, and was more based on guessing. Could her belief that she was having a girl changed her hormones to make me more susceptible to the nature aspects? It’s a question I don’t think I’ll ever be able to answer. (She also told me she had a different gynecologist for my older sister than for myself and my two younger brothers. lol)