is it more likely that a person can be stuck by lightning while standing below a tall tree rather than a short one

Yes, a person standing below a tall tree has greater risk of getting struck by lightning than a person standing below a short one. Sometimes during a thunderstorm, when clouds get charged, the positive charges accumulate near the top of the clouds while the negative charges accumulate at the bottom. Since opposite charges attract each other, the negative charges attract the positive charges of objects near the ground. These positive charges accumulate at the topmost point of the objects.Thus positive charges accumulated at the top of a tall tree are closer to the clouds than the ones at the top of a smaller tree. So when a lightning strikes, it strikes the taller tree (if the tree is the tallest object in that area), which conducts the charges and shocks the person taking shelter under it. So it is always advisable to take shelter under a smaller tree if taller trees are there, or just better to avoid standing near trees altogether in the event of a thunderstorm.