def METHOD_NAME(dice_ast: d20.ast.Node, critdice: int):
    """A function that finds the size of left most Dice AST node and generates crit dice based on that, for
    crit types that double all original dice, but not any additional crit dice. By finding the left most dice,
    we do our best to ensure its based on the weapon/source and not any other additional bonuses."""
    left = d20.utils.leftmost(dice_ast)
    # if we're at the bottom of the branch and it's the dice, add *critdice*
    if isinstance(left, d20.ast.Dice):
        return d20.ast.Dice(critdice, left.size)