Run any recursive function and see your tree of a function calls.
 • choose a recursive function from the templates, or write your own
 • make sure there is only ONE function definition
 • call the function with an argument
 • don't use too high of an argument - the tree may be too big
 • in the recursion tree, click a node to see what the call returns
  blue node = function call with recursion
  purple node = base case
  green node = memoized value