Trees and Binary Search Trees useing arraylist

im trying to do a poject where Im using a arrayList to make a BST. im assigning my frist variable as the parent so at 0 in the array, my question is how can I then add a right leaf to that in spot 2 without already having a left leaf of spot 1? this is what I currently have and I keep getting the java.lang.IndexOutOfBoundsException

import java.util.ArrayList;

public class test{

/**
 * @param args the command line arguments
 */
public static void main(String[] args) {
    // TODO code application logic here
    myData a = new myData(2, 'B', "joe:smo");
    myData b = new myData(7, 'B', "joe:smo");
    myData c = new myData(5, 'B', "joe:smo");
    myData d = new myData(2, 'B', "joe:smo");
    myData e = new myData(6, 'B', "joe:smo");
    myData f = new myData(9, 'B', "joe:smo");
    myData g = new myData(5, 'B', "joe:smo");
    myData h = new myData(11, 'B', "joe:smo");
    myData i = new myData(4, 'B', "joe:smo");
    
    
    BinaryStreeImplicit tree = new BinaryStreeImplicit();
    
    tree.root(a);
    tree.insert(b);
    tree.insert(c);
    tree.insert(d);
    tree.insert(e);
    tree.insert(f);
    tree.insert(g);
    tree.insert(h);
    tree.insert(i);
    tree.print();

}

static class BinaryStreeImplicit {

    int root = 0;
    ArrayList<myData> data = new ArrayList<myData>();
    int treeSize = 0;
    int lastIndex = 0;
    public void root(myData x) {
        data.add(x);
    }

    public void print() {
        for (int i = 0; i < data.size(); i++) {
            System.out.println(data.get(i).courseNumber);
        }
    }

    public void insert(myData x) {
        int n = 0;
        int r = 1;
        while (r == 1) {
            if (x.courseNumber < data.get(n).courseNumber) {
                n = (root * 2) + 1;
                if (data.get(n) == null) {
                    
                    data.set(n, x);
                    r = 0;
                    treeSize++;
                }
            } else {
                n = (root * 2) + 2;
                if (data.get(n) == null) {
                    data.set(n, x);
                    r = 0;
                    treeSize++;
                }

            }
        }
    }
}

myData class looks like this

public class myData {
int courseNumber;
char grade;
String stuName;

public myData(int courseNumber, char grade, String stuName) {
    this.courseNumber = courseNumber;
    this.grade = grade;
    this.stuName = stuName;
    
    
}

public int getCourseNumber() {
    return courseNumber;
}

public char getGrade() {
    return grade;
}

public String getStuName() {
    return stuName;
}