1. A search tree can be represented in python as follows: (a) if the search tree contains a single leaf node L, it can be represented by non-tuple object L (b) if the search tree has more than one node and is rooted at N, then it can be represented by a tuple (S1 S2.Sk ) where Si represents the i th subtree of N. Consider for example the following search trees, whose python representations are shown later. Write a single Python function, called BFS. It takes a single argument FRINGE that represents a list of search trees, and returns a top-level list of leaf nodes, in the order they are visited by left-to-right breadth-first search. The inital call to BFS passes a FRINGE list with a single element: the root of the search tree. Test your program on at least these inputs