Java comparing generic types

You can use this simple approach
for data greater than root.getData = 1, for data equals root.getData = 0,for data lesser than root.getData = -1

public class BST<E extends Number & Comparable<? super E>>{
    void add(){
    ...
    if(data.compareTo(root.getData()) == 1)
    ...
}

You cannot overload operators in Java. The < operator only applies to primitive (or numeric) types, not reference types. Since T is a type variable that represents a reference type, you cannot use < on variables of type T. You have to use

if (item.compareTo(bn.item) < 0) 

check the value returned and decide to do what you wish with it.

You don't know what the type T will be but you know that it will be a type that implements Comparable and therefore implements the compareTo() method.