Rajiv, you can't do that is tree is by parent pointers. you need to bubble up from the given nodes and put parents to a hash.

For each node traversed from the root, if both values are less than the current Node, then move to the left if both values are greater than the currentNode, then move to the right, if the value of current Node is between value 1 and value 2, then you have found the nearest common ancestor.