Turtlestein

Hello, sorry if there is an obvious answer. I am attempting to print two models stacked on top of each other. But when ever I bring in the second model It doesn't get included when I hit slice. It is just greyed out even though it builds a tree support. It there something I need to do to models that I bring in with the original model to make it part of it? Attached is my project. I am trying to put the hat on the letter I. The hat slices fine when opened by itself. Thanks for the help Wizard project v2.3mf