Comparing two generics in compareTo()

I have the following class signatures:

public class SkipListSet<T extends Comparable<T>> implements SortedSet<T>

and another class outside of SkipListSet class:

class Node<T extends Comparable<T>>

The second one acts as a wrapper class that contains the following:

        T data;
        List<Node<T>> tower;
        Node<T> nextNode = null;
        Node<T> prevNode = null;

When I try implementing compareTo() method in my Node class:

        public int compareTo(T somePayLoad) {
            if (this.data < somePayLoad)
                return -1;
            else if (this.data > somePayLoad)
                return 1;
            else
                return 0;
        }

I get the following error:

SkipListSet.java:171: error: bad operand types for binary operator '<'
                        if (this.data < somePayLoad)
                                      ^
  first type:  T
  second type: T
  where T is a type-variable:
    T extends Comparable<T> declared in class SkipListSet.Node

Why is it that I can’t compare two types of T data in my compareTo method?

    TestSkipListSet<NodeData> list = new TestSkipListSet<NodeData>();
    TestSkipListSet<NodeData2> list2 = new TestSkipListSet<NodeData2>();

    class NodeData implements Comparable<NodeData> {
        int value;
        @Override
        public int compareTo(@NonNull NodeData o) {
            return this.value - o.value;
        }
    }

    class NodeData2 implements Comparable<NodeData2> {
        TestUser value;
        @Override
        public int compareTo(@NonNull NodeData2 o) {
            return this.value.age-o.value.age;
        }
    }
    class TestUser{
        int age;
    }

    public class TestSkipListSet<T extends Comparable<T>> implements SortedSet<T>{
       ...
    }

public int compareTo(T somePayLoad) {

    return this.data.compareTo(somePayLoad.data);
}