The great Tree List recursion problem

import java.util.*;

class Node{
String data;
Node left;
Node right;
boolean isVisited;
Node(String data,Node left,Node right){
this.data=data;
this.left=left;
this.right=right;
this.isVisited=false;
}
}


class LL{
Node head;
Node tail;
}

class Main{

Stack<Node> st = new Stack<Node>();
int pIndex=0;
String pre[]={"A","B","D","E","F","C","G","H"};
String in[]={"D","B","F","E","A","C","H","G"};

Node buildTree(int start , int end){
if(start>end){
return null;
}

Node t=new Node(pre[pIndex],null,null);

pIndex++;
int iIndex=search(t.data);

if(start == end){
t.left=null;
t.right=null;
}
else{
t.left=buildTree(start,iIndex-1);
t.right=buildTree(iIndex+1,end);
}

return t;
}

int search(String str){
for(int i=0;i<in.length;i++){
if(in[i] == str){
return i;
}
}
return -1;
}

void printInTree(Node t){
if(t!=null){
printInTree(t.left);
System.out.print(" "+t.data);
printInTree(t.right);
}
}


LL fun(Node root,LL linkedList){
//System.out.println("doing for "+root.data);


if(root == null){
linkedList.head=null;
linkedList.tail=null;
return null;
}

if (root.left == null && root.right == null){
linkedList.head=root;
linkedList.tail=root;
return linkedList;
}

if(root.left != null){
//System.out.println("checking left of "+root.data);
LL linkedList1=new LL();
linkedList1.head=null;
linkedList1.tail=null;


fun(root.left,linkedList1);

/*if(linkedList1.head != null){
System.out.println("after returning form left of "+root.data +"the values of head1 is "+linkedList1.head.data);
}
else{
System.out.println("after returning form right of "+root.data +"the values of head1 is NULL");
}
if(linkedList1.tail != null){
System.out.println("after returning form left of "+root.data+ " the values of tail1 is "+linkedList1.tail.data);
}
else{
System.out.println("after returning form right of "+root.data +"the values of tail1 is NULL");
}

printLL(linkedList1);
*/

root.left=linkedList1.tail;
root.left.right=root;
linkedList.head=linkedList1.head;
//linkedList.head=linkedList1.head;
}

if(root.right != null){
LL linkedList2=new LL();
linkedList2.head=null;
linkedList2.tail=null;

fun(root.right,linkedList2);

/*if(linkedList2.head != null){
System.out.println("after returning form right of "+root.data +"the values of head2 is "+linkedList2.head.data);
}
else{
System.out.println("after returning form right of "+root.data +"the values of head2 is NULL");
}
if(linkedList2.tail != null){
System.out.println("after returning form right of "+root.data+ " the values of tail2 is "+linkedList2.tail.data);
}
else{
System.out.println("after returning form right of "+root.data +"the values of tail2 is NULL");
}
printLL(linkedList2);
*/

root.right=linkedList2.head;
root.right.left=root;

linkedList.tail=linkedList2.tail;


//linkedList.tail=linkedList2.tail;

}

if(linkedList.head != null && linkedList.tail ==null){ //
  linkedList.tail=root;
}
if(linkedList.head == null && linkedList.tail !=null){
linkedList.head=root;
}

return linkedList;

}

void printLL(LL linkedList){
Node head=linkedList.head;
Node tail=linkedList.tail;

while(head!=tail){
System.out.print("-"+head.data);

head=head.right;
}

if(head!=null){
System.out.print("-"+head.data);
}

}

public static void main(String args[]){

Main m=new Main();

Node root=m.buildTree(0,m.pre.length-1);
System.out.println(root.data);
//m.printInTree(root);
//m.printInTreeWOStack(root);

LL linkedList=new LL();
linkedList.head=null;
linkedList.tail=null;

LL t=m.fun(root,linkedList);
System.out.println();
System.out.println();
m.printLL(linkedList);
System.out.println();


}
}