The reason your tongue sticks to a metal pole and not a wooden pole on cold winter days is due to how the material conducts heat also known as thermal conduction.
Wood doesn't do thermal conduction the way metal does so that's why your tongue sticks to metal since metal is a good conductor of heat whereas a wooden pole is not.
Heat that comes from your tongue (including the moisture) is absorbed faster than your body can replenish it and this then has the effect of freezing your saliva in the tongue's pores to the metal surface.
To remove your tongue from a metal pole or metal surface you either pour some warm water over the tongue or cold water over the tongue to help remove the tongue.
Never try to pull it free without adding some water or either warm or cold because it can tear your tongue.
If you're stuck by yourself on the pole and have a cell phone call 911 and get some help if you can because the fire department and ambulance people know how to get your tongue removed from the pole.