Original Watergate Salad

large ( 1 pound 4 ounce ) can of crushed pineapple , in 100% pineapple juice, drained - reserve the juice

small packages of instant pistachio pudding mix

large ( 16 ounce ) tub of non-dairy topping (like Cool Whip ), thawed

miniature marshmallows

chopped pecans or walnuts, optional