The water reaches to the top most part of a tree due to the transpirational pull during day 
time. What makes water rise upwards during night?    

Evaporation of water molecules from the cells of a leaf creates a suction which pulls water from the xylem cells of roots. This leads to an uptake of water from the soil through roots. The whole event causes rise of water and dissolved minerals up to the top of a tall tree. During the day the pull is low but during night time it is fast. During night time transpiration is fast and transpiration create a pressure also called transpirational pull which cause root water to move at leaves.