public interface BinaryTreeInterface<E extends Comparable<E>> 
{
    /**
     * 
     * @return the number of items in the tree
     */
    int size();
    
    /**
     *  
     * @return the maximum number of links between 
     *  the root of the tree and the most distant leaf
     */
    int maxDepth();
    
    /**
     * 
     * @return return true if the tree has no nodes
     */
    boolean isEmpty();
    
    /**
     * @return true if the given element exists in the tree and false otherwise
     */
    boolean contains(E element);
    
    /**
     * Add an element to the tree (if the element does not already exist
     * in the tree) If the element already is in the tree, do nothing.
     * @param element the element to be added
     */
    void insert(E element);
    
    /**
     * Remove something from the tree
     * @param element the element to be removed
     * @return element if it was in the tree, null otherwise
     */
    E remove(E element);
}