Drain olives. Cut block of cheese horizontally into 2 pieces, each about 1/2 inch thick. Cut cheese with 1-inch star-shape canapé cutter. Cover cheese stars with plastic wrap.
Break toothpicks in half as needed; push each olive onto toothpick half. Starting at bottom of cone, insert toothpicks until they stay securely in place. Continue placing olives in random order on tree, varying sizes and leaving spaces for the cheese stars. (For stability of the tree, place most of the larger olives near the bottom.)
Push each cheese star onto toothpick half; insert into cone among the olives. Top tree with a cheese star that has been inserted horizontally on toothpick between points of star. Insert rosemary sprigs randomly between olives and cheese. Cover loosely and refrigerate no longer than 8 hours before serving.