It's just something that I've always enjoyed doing.
Especially as a child I remember thinking how much easier of a life women had(nowadays my views are different).
But that was one of the factors, I think. Not wanting to take on the expectations that the society sets on men.
Currently, I enjoy the thrill & shocking my peers. I also feel extremely comfortable and free in women's clothing.
So, what first lit the spark was the fact that I felt discouraged by the gender-norms that I would have to fulfill in the future.