Class for avl trees in c++

So I wanted to make an avl tree in c++.I used a class to make the nodes and a class for the rest of the fuctions ( instert,delete etc).When I want to make more than one trees I decided that i needed to make more roots(one for every tree).The problem is when I declare the new root inside the main.When i declare it outside it seems to work fine. This is the class

class avl_node

{
public:
int data;

avl_node *left;

avl_node *right;

}*root;

and this is the main

int main()

{
avl_node *roott;
int item;   
avlTree avl;
avlTree kk;               
root=avl.insert(root,item);          
roott=kk.insert(roott,item);         
kk.display(roott, 1);
return 0;
}