// merge two binary tree using recursive function
function mergeTwoBT(t1,t2){
if(t1==null)return t2;
if(t2==null)return t1;
t1.data= t1.data + t2.data
t1.left =mergeTwoBT(t1.left,t2.left);
t1.right =mergeTwoBT(t1.right,t2.right);
return t1 ;
}