ReactJS why onClick is going to trigger two methods instead of one [duplicate]

I have two methods addItem and removeItem. I have also two buttons for these methods via onClick. When I click on addItem button then both methods are triggered, please why?

<button id="a" type="button" onClick={addItem} className="button button-size-small">Add to cart</button>

{items.map((item, index) => {

    <button id="b" type="button" onClick={removeItem(item)}>Delete</button>

})}


const addItem = _ => {
        const item = { id: (new Date).getTime(), userId, choosedFlavor, amount };
        setItems([...items, item]);
    }

const removeItem = item => {
       console.log('remove', item);
    }