Simple walk through of an array list is giving me an out off bounds exception .

I have created an arrarylist which holds the height of 10,000 binarysearchtrees I'm simply trying to print the height of every tree out of the arraylist. However at index[50000] it is giving me the error. But i print the size of the arraylist before and it is 10000 i just can't figure this out.Any ideas why this is happening would be great

====================code=========================

import java.util.Random;
import java.util.ArrayList;
import java.util.Collections;

public class RandomGenerator
{

      public static void main(String [] args)
      {
        ArrayList binarylist = new ArrayList();
        ArrayList Avllist = new ArrayList();

          AvlTree a;
          BinarySearchTree b ;
          Random random = new Random();
        int numtrees =   10000;              //Integer.parseInt(args[0]);
        int sizetrees =   100;            //Integer.parseInt(args[1]);

        //create binary trees
          for (int i=0; i < numtrees ;i++)
          {
                  b = new BinarySearchTree();
            a = new AvlTree();

                //create # int's inside tree
                  for(int j=0; j < sizetrees; j++)
                  {
                    b.insert(random.nextInt() );
                    a.insert(random.nextInt() );

                }


          binarylist.add(new Integer(b.height()) );
          Avllist.add(new Integer(a.getHeight(a.getRoot() ) ) );


            }



     Collections.sort(binarylist);

     for(int i=0; i < numtrees ; i++)
     {
             System.out.println( binarylist.get(i) );

             binarylist.remove(i);
       }



System.out.println(binarylist.size() + " " +  binarylist.get(4999) );






}