I have writen a pine code that i am going to use in trade view, it says a Error at 4:15 Syntax error at input '('

Question

//@version=5

// Define the sell signal
def sellSignal():
    return crossunder(close, BollingerBands(
            source=close,
            length=20,
            window_dev=2.5,
            matype="sma",
        ))

// Define the buy signal
def buySignal():
    return crossover(close, BollingerBands(
            source=close,
            length=20,
            window_dev=2.5,
            matype="sma",
        ))

// Plot the sell signal with a red symbol
plot(sellSignal(), color=color.red, linewidth=2, style=plot.style_areabr)

// Plot the buy signal with a green symbol
plot(buySignal(), color=color.green, linewidth=2, style=plot.style_areabr)

i tried this code to make a indicator on trade view, which can tell me when to buy and when to sell my trade, by merging ai in my indicator