Ok, the quick and dirty explanation is to make your primary BST have a BST container ie:
private class Node{
Node left, right;
String data;
BST secondaryBST = new BST();
}
and then whenever you want to have access to the secondary BST method just use a code like "node.secondaryBST.method()"
I hope that make sense, if anyone need more explanation just let me know.