wc-add-depending-cart-total.php

/**
 * Add another product depending on the cart total.
 */
function wb_add_product_to_cart() {
	if ( ! is_admin() ) {
		global $woocommerce;
		$product_id = 38; // replace with your product id.
		$found      = false;
		$cart_total = 30; // replace with your cart total needed to add above item.

		if ( $woocommerce->cart->total >= $cart_total ) {
			// check if product already in cart.
			if ( sizeof( $woocommerce->cart->get_cart() ) > 0 ) {
				foreach ( $woocommerce->cart->get_cart() as $cart_item_key => $values ) {
					$_product = $values['data'];
					if ( $_product->get_id() == $product_id ) {
						$found = true;
					}
				}
				// if product not found, add it.
				if ( ! $found ) {
					$woocommerce->cart->add_to_cart( $product_id );
				}
			} else {
				// if no products in cart, add it.
				$woocommerce->cart->add_to_cart( $product_id );
			}
		}
	}
}
add_action( 'template_redirect', 'wb_add_product_to_cart' );