Generate an expression where each leaf might have a different depth between min_ and max_.

        Parameters
        ----------
        pset: PrimitiveSetTyped
            Primitive set from which primitives are selected.
        min_: int
            Minimum height of the produced trees.
        max_: int
            Maximum Height of the produced trees.
        type_: class
            The type that should return the tree when called, when
                  :obj:None (default) the type of :pset: (pset.ret)
                  is assumed.
        Returns
        -------
        individual: list
            A grown tree with leaves at possibly different depths.

def _gen_grow_safe(self, pset, min_, max_, type_=None):
        """Generate an expression where each leaf might have a different depth between min_ and max_.

        Parameters
        ----------
        pset: PrimitiveSetTyped
            Primitive set from which primitives are selected.
        min_: int
            Minimum height of the produced trees.
        max_: int
            Maximum Height of the produced trees.
        type_: class
            The type that should return the tree when called, when
                  :obj:None (default) the type of :pset: (pset.ret)
                  is assumed.
        Returns
        -------
        individual: list
            A grown tree with leaves at possibly different depths.
        """

        def condition(height, depth, type_):
            """Stop when the depth is equal to height or when a node should be a terminal."""
            return type_ not in self.ret_types or depth == height

        return self._generate(pset, min_, max_, condition, type_)