| You dont need a humidifier a decent water bowl is fine and maybe a spray or spill some water around shedding time. For hatchies a heat cord under a platic tub is good for heating. As the get into a bigger enclosure i like to give them a hot basking spot(mine would be somewhere around 45C at a guess) and the rest of the enclosure is roughly at room temperature.
There have been a fair few threads on these snakes just do a search on this site for common/green tree snakes and you should find heaps of helpful info. | 
