Validate BinarySearchTree

public boolean isValidBST(BTreeNode root) {
if(root==null)
return true;

return recurse(root, Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY);
}

public boolean recurse(BTreeNode root, double low, double high){

if(root.val<=low || root.val>=high)
return false;

if(root.left!=null && !recurse(root.left, low, root.val))
return false;

if(root.right!=null && !recurse(root.right, root.val, high))
return false;

return true;
}