I only know one person in real life who is bigender. She presents as fully masculine when in boy mode, and fully feminine when she is in girl mode. Her expression is quite binary: she is always one or the other, never both. She is in the military (Canadian), so she wears male uniform in boy mode and female uniform when in girl mode.
Personally, I am quite binary female-only, so boy mode never comes up any more. But when I was transitioning, I would present like my friend does: either one or the other, never in-between. Which gender I presented as depended on where I was going and what I was doing.