Tree displays recursive values

Hello, I am new to ExtJS and there is a bug that I need to fix. Our application has a tree like:

Node 1

Node 2

When all nodes are expanded, it looks like:

Node 1

Unit 1

Component 1

Component 2

Unit 2

Component 3

Node 2

Unit 3

Component 4

We use NodeTreeStore, UnitTreeStore and ComponentTreeStore. They all use proxy URL to get data in XML format.

In the tree, a listener beforeitemexpand is defined to append childNodes based on the node type. For example:

if (node.data.type == 'node') {

var Unitlength = UnitStore.getRootNode().childNodes.length;

for (var j=0; j<=(Unitlength -1); j++){

if (node.get('name') == UnitStore.getRootNode().getChildAt(j).get('node')){

node.appendChild(UnitStore.getRootNode().getChildAt(j));

Unitlength = Unitlength-1;

j = j-1;

}

}

}

Now the problem is when the tree is loaded, sometimes not all the nodes are loaded. If I expand a node that is not loaded, it takes a while, then displays recursive values:

Node 1

Node 1

Node 2

Node 2

How can I get around with this problem? Thank you!

Tree displays recursive values