import re


def remove_chars_re(string: str) -> str:
    """Remove all charactes but strings (with regex support).

    Args:
        string: <str> input string.

    Returns:
        string: <str> sorted only letters.

    Examples:
        >>> assert remove_chars_re('.tree1') == 'tree'
    """

    return re.sub(pattern='[^a-zA-Z ]', repl='', string=string)