Pseudo Code is something like this -
current = -infinite;
inorder(node, treeType)
{
if node == null then return;
inorder(node->left, treeType);
if current >= node->data then treeType = "No BST"
current = node-> data;
inorder(node->right, treeType);
}
Call the function something like
inorder(head, "BST");