'Converts a tree to string without translations.
Examples
>>> from sympy.abc import x, y, z
>>> from sympy import Integral, sin
>>> from sympy.plotting.experimental_lambdify import Lambdifier
>>> str2tree = Lambdifier([x], x).str2tree
>>> tree2str = Lambdifier([x], x).tree2str
>>> tree2str(str2tree(str(x+y*sin(z)+1)))
\'x + y*sin(z) + 1\''

@classmethod
def tree2str(cls, tree):

    if isinstance(tree, str):
        return tree
    else:
        return ''.join(map(cls.tree2str, tree))
