The Pile of Gifts is an event that appears during a temporary event expedition and can be used to gain nice rewards. By increasing its levels, you enhance the rewards you'll receive at the end of the expedition.

You can upgrade the Pile of Gifts using tokens found on the expedition map .  Even if you haven't fully upgraded the Pile, you will receive its prizes but only by the end of the expedition. However, if you max out its upgrades, you will be able to obtain rewards before the expedition ends.