def get_edges(tree):
    """
    Get edges of the tree in the form of (node_start,node_end)
    :param tree: ETE tree
    :return: List of edges of a tree of a list of tuples (node_start,node_end)
    """
    edges = []
    for node in tree.traverse('postorder'):
        if not node.is_leaf():
            edges.append((node, node.children[0]))
            edges.append((node, node.children[1]))
    return edges
