They're rear fanged so you would have to force your finger down it's throat to be envenomated!
Actually Common Tree Snakes are solid-toothed and are considered to be harmless - Brown Tree Snakes are rear-fanged and mildly-venomous. As for forcing your finger down their throat, I basically did that ... http://www.aussiepythons.com/forum/australian-snakes-37/common-tree-snakes-venomous-tag-143636/