Implementing TreeModel
public class PMEntry implements TreeModel{

private String title;
private List<PMEntry> pmEntryCollection;
private String pmId;
private String href;
private PMEntry root;
private ModuleType type;

public PMEntry (PMEntry root){

  this.root = root;
}

@Override
public Object getRoot() {

   return ((PMEntry)this.root);
}

@Override
public Object getChild(Object o, int i) {


    if(getPmEntryCollection().isEmpty()){

        return null;

    }else {

      return (PMEntry) getPmEntryCollection().get(i);

    }
}

@Override
public int getChildCount(Object o) {

   if(getPmEntryCollection().isEmpty()){

        return 0;

    }else {

      return getPmEntryCollection().size();

    }
}

@Override
public boolean isLeaf(Object o) {
    PMEntry pmentry = (PMEntry)o;
    return (pmentry.getType() == ModuleType.DM) ? true : false;
 }

@Override
public void valueForPathChanged(TreePath tp, Object o) {
   //todo
}

@Override
public int getIndexOfChild(Object parent, Object child) {

    if (!(parent instanceof PMEntry)){

        System.out.println("Returning -1");
        return -1;
    }

    PMEntry pParent = (PMEntry) parent;

    List<PMEntry> children = pParent.getPmEntryCollection();

    if (children == null) {
        System.out.println("children = null, Returning -1");
        return -1;

    }

    for (int i = 0; i < children.size(); i++) {

        System.out.println("Child:" + child);

        if (children.get(i) == child) {

            return i;
        }

    }

    return -1;
}

@Override
public void addTreeModelListener(TreeModelListener tl) {
   //todo
}

@Override
public void removeTreeModelListener(TreeModelListener tl) {
    //todo
}

@Override
public String toString(){

    return this.getTitle();
}
public enum ModuleType {

    PM,
    DM

}

// getters and setters here....

PMEntry tm = new PMEntry(null);
tm.setTitle("Root");

PMEntry pmRoot = new PMEntry((PMEntry)(tm));
pmRoot.setTitle("Project");

PMEntry pm1 = new PMEntry(pmRoot);
pm1.setType(PMEntry.ModuleType.DM);
pm1.setTitle("Publication Module");

PMEntry pm2 = new PMEntry(pmRoot);
pm2.setType(PMEntry.ModuleType.PM);
pm2.setTitle("Chapter");

List<PMEntry> pmCollection = new ArrayList<PMEntry>();
List<PMEntry> pmCollection1 = new ArrayList<PMEntry>();

PMEntry pm3 = new PMEntry(null);
pm3.setType(PMEntry.ModuleType.DM);
pm3.setTitle("Data Module");

PMEntry pm4 = new PMEntry(null);
pm4.setType(PMEntry.ModuleType.DM);
pm4.setTitle("Data Module");

pmCollection1.add(pm3);
pmCollection1.add(pm4);

pm2.setPmEntryCollection(pmCollection1);

pmCollection.add(pm1);
pmCollection.add(pm2);

pmRoot.setPmEntryCollection(pmCollection);

this.jTree1.setModel(pmRoot);