Could have sworn I read all league info text in-game

So I stand at the tree thingy and I have the item thingy and I clicked a socket thingy and I pop the item thingy in the socket thingy and the item thingy remains in my inventory and is not slotted to the socket thingy.

Send help.

item thingy "growing womb gift"
tree thingy "the genesis tree"
socket thingy "graft item womb"


Click to place a growing womb gift in this womb

How do I make that stick and stay in there? Is this item supposed to go in several slots?