Deserializing an abstract class in Gson

I have a tree object in JSON format I'm trying to deserialize with Gson. Each node contains its child nodes as fields of object type Node. Node is an interface, which has several concrete class implementations. During the deserialization process, how can I communicate to Gson which concrete class to implement when deserializing the node, if I do not know a priori which type the node belongs to? Each Node has a member field specifying the type. Is there a way to access the field when the object is in serialized form, and somehow communicate the type to Gson?

Thanks!