You can't (easily) deserialize those maps in Go, because the serialized data contains Java-specific data, data required to instantiate and initialize the original Java class (java.util.TreeMap in this case), which is obviously unknown to a Go app. Java object serialization and the encoding implemented by encoding/gob have nothing to do with each other; the former is specific to Java and the latter is specific to Go.
Instead try to serialize the Java object in a language-neutral way, e.g. to JSON, which you can decode in Go (or in any other language).