public static function recurse( $array, $array1 ) {
		foreach ( $array1 as $key => $value ) {

			// Create new key in $array, if it is empty or not an array.
			if ( ! isset( $array[ $key ] ) || ( isset( $array[ $key ] ) && ! is_array( $array[ $key ] ) ) ) {
				$array[ $key ] = [];
			}

			// Overwrite the value in the base array.
			if ( is_array( $value ) ) {
				$value = self::recurse( $array[ $key ], $value );
			}
			$array[ $key ] = $value;
		}
		return $array;
	}