def retrieve_tree(i):
    """
    (function) retrieve_tree
    ------------------------
    Retrieve the tree

    Parameter
    ---------
    - i : tree index

    Return
    ------
    - selected tree
    """
    tree_list = [{'no surfacing': {0: 'no', 1: {'flippers': {0: 'no', 1: 'yes'}}}},
                {'no surfacing': {0: 'no', 1: {'flippers': {0: {'head': {0: 'no', 1: 'yes'}}, 1: 'no'}}}}]

    return tree_list[i]