Unity - UI Inventory / InventorySlot new item comand?

in my case my code when breaking the tree it quanha item drop chances, but I just managed to create new slot, what I want to do is select a empty slot and add new item

foreach (ItemDropChance itemChance in dropChances)
if (Random.value <= itemChance.probability)
player.inventory.Add(new ItemSlot(new Item(itemChance.item)));

foreach (ItemDropChance itemChance in dropChances)
if (Random.value <= itemChance.probability)

                player.inventory(new ItemSlot (new Item(itemChance.item)));