How does a repeating element behave when added to a TreeSet?

In Java, TreeSet is a set that stores elements in sorted order and does not allow duplicates. When attempting to add a duplicate element (add returns false), it will not be added because a set cannot contain identical elements.

Example:

TreeSet<Integer> set = new TreeSet<>();
set.add(5); // true
set.add(3); // true
boolean added = set.add(5); // false, element 5 already exists
System.out.println(set); // [3, 5]

Thus, duplicate elements are ignored and the set remains unchanged.