Dialog Flow Chart/Tree

[Shez]

I've been busy creating my own game script (in its entirety - as portfolio material for job applications) but am unsure how to procede with writing/creating dialog trees. By 'dialog trees' I mean the dialog spoken by NPCs and the corresponding player responces that can lead to any number of different conversation endings. Right now I've written the dialog connected by arrows to the responces, followed by more arrows to the NPC response.

Is there a standard format for dialog trees or does every writer just wing it? Are there any good especially good resources for game writers?