It is my (wholly unsubstantiated) guess that the majority of Soviet personnel in Vietnam are in fact not Russian.
( It ( ( is ( ( my ( ( -LRB- ( ( wholly unsubstantiated ) -RRB- ) ) guess ) ) ( that ( ( ( the majority ) ( of ( ( Soviet personnel ) ( in Vietnam ) ) ) ) ( ( are ( in fact ) ) ( not Russian ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VBZ is) (NP (NP (PRP$ my) (PRN (-LRB- -LRB-) (ADJP (RB wholly) (JJ unsubstantiated)) (-RRB- -RRB-)) (NN guess)) (SBAR (IN that) (S (NP (NP (DT the) (NN majority)) (PP (IN of) (NP (NP (JJ Soviet) (NNS personnel)) (PP (IN in) (NP (NNP Vietnam)))))) (VP (VBP are) (ADVP (IN in) (NN fact)) (ADJP (RB not) (JJ Russian))))))) (. .)))
I guess that most Soviets in Vietnam are not Russian
( I ( guess ( that ( ( ( most Soviets ) ( in Vietnam ) ) ( ( are not ) Russian ) ) ) ) )
(ROOT (S (NP (PRP I)) (VP (VBP guess) (SBAR (IN that) (S (NP (NP (JJS most) (NNS Soviets)) (PP (IN in) (NP (NNP Vietnam)))) (VP (VBP are) (RB not) (ADJP (JJ Russian))))))))