Error java.lang.Integer is not within bounds of type-variable T; BinarySearchTree

I want to create a simple Binary Search Tree which uses generics to specify the data type. However, when I want to create a new tree of Integers, I get the following error:

type argument java.lang.Integer is not within bounds of type-variable T

I tried other data types which are clearly extending Comparable, so why is this not working?

Here is my code:

Interface:

public interface Comparable<T>
{
    int compareTo( T t );
}

BinarySearchTree:

public class BinarySearchTree<T extends Comparable<T>>
{
private T content;
private BinarySearchTree<T> leftChild, rightChild;

public BinarySearchTree()
{
    content = null;
    leftChild = null;
    rightChild = null;
}

public T getContent()     
{
    if(!isEmpty())
    {
        return content;
    }
    else
    {
        throw new RuntimeException();
    }
}

public boolean isEmpty()
{
    return content == null;
}

public boolean isLeaf()
{
    return !isEmpty() && leftChild.isEmpty() && rightChild.isEmpty();
}

public void add(T t)
{
    if(isEmpty())
    {
        content = t;
        leftChild = new BinarySearchTree<T>();
        rightChild = new BinarySearchTree<T>();
    }
    else
    {
        if(content.compareTo(t) > 0)
        {
            leftChild.add(t);
        }
        if(content.compareTo(t) < 0)
        {
            rightChild.add(t);
        }
    }
} 

public int size()
{
    if(isEmpty())
    {
        return 0;
    }
    else
    {
        return 1 + leftChild.size() + rightChild.size();
    }
}

public boolean contains(T t)
{
    if(isEmpty())
    {
        return false;
    }
    else
    {
        if(content.compareTo(t) > 0)
            leftChild.contains(t);
        else if(content.compareTo(t) < 0)
            rightChild.contains(t);
        return true;
    }
}

public void show()
{
    if(!isEmpty())
    {
        leftChild.show();
        System.out.println(content);
        rightChild.show();
    }
}

}

Main:

public class main
{

public static void main(String[] args)
{
    test();
}

public static void test()
{
    BinarySearchTree<Integer> tree = new BinarySearchTree<>();
    tree.add("5");
    tree.add("10");
    tree.add("3");
    tree.add("1");
    tree.show();
}
}

The error comes with this line: BinarySearchTree<Integer> tree = new BinarySearchTree<>();