Drift on simple take off and ascend

#1

I got my drone to take off and ascend, however it seems to drift off to one side even though I’m simply pushing the trottle forward/up. My expectations were that it would simply ascend straight up. Any ideas on what I’m doing wrong?

#2

Take a look here for info on trim. There are probably other sources on trimming a quad copter (e.g., youtube). Hope this helps.