Huh! In my speech, the Tr in "tree" or "trigger" is really close to Chr as in "chree". In fact to pronounce "chree" I have to aspirate so hard to distinguish it from /tr/.

Is this common? [ˈt͡ʃɹi:] instead of [ˈtɹi:]? Why does this happen? Is there something about going from a plosive to an approximant that creates an affricate?