Thread: ClassCastException: Vehicle cannot be cast to java.base/java.lang.Comparable

package HRT;
 
import java.util.TreeSet;
 
public class Vehicle {
    String type ;
     double speed;
 
 
    public Vehicle() {
        type = "bicycle";
        speed = 20.0 ;
    }
    public Vehicle(String type, double speed) {
        this.type= type ;
        this.speed=speed;
    }
 
 
 
public static String setType(String type)   {
    return type;
}
public static double setSpeed(double speed) {
    return speed;
 
}
public void speedUp() {
    speed = speed *2;
 
}
public void speedDown() {
    speed = speed/2 ;
 
}
 
}
 
package HRT;
 
import java.util.TreeSet;
 
 
public static void partB() {
         String[] typeArray = {"car", "train", "plane", "bicycle",};
         double[] speedArray = {60, 180, 1000, 20};
         TreeSet vehicles = new TreeSet<>();
         for(int i = 0; i < typeArray.length; i++) {
         vehicles.add(new Vehicle(typeArray[i], speedArray[i]));
         }
        }
 
public static void main(String[] args) { 
        Exercise4.partB();
    }   
}

How can I modify the class Vehicle to make the program run correctly ?
I don't understand why i get this ClassCastException
can anyone help please ?

Is this correct?

package HRT;
 
import java.util.TreeSet;
 
public class Vehicle implements Comparable {
	String type ;
	 double speed;
 
 
	public Vehicle() {
		type = "bicycle";
		speed = 20.0 ;
	}
	public Vehicle(String type, double speed) {
		this.type= type ;
		this.speed=speed;
	}
 
 
 
public static String setType(String type)	{
	return type;
}
public static double setSpeed(double speed) {
	return speed;
 
}
public void speedUp() {
	speed = speed *2;
 
}
public void speedDown() {
	speed = speed/2 ;
 
}
 
public int compareTo(Object temp) {
	Vehicle other = (Vehicle) temp;
	if (speed > other.speed)
	{
		return 1;
	}
	else if(speed < other.speed) {
		return -1;
	}
	else return 0;
 
 
}
 
}