Treason against the United States, shall consist only in levying War against them, or in adhering to their Enemies, giving them Aid and Comfort. No Person shall be convicted of Treason unless on the Testimony of two Witnesses to the same overt Act, or on Confession in open Court.
First, he is guilty of espionage, by intentionally gaining "secrets" for the sole purpose of sharing those secrets - supposedly he admitted he took his job solely in order to gain "secret" information.
He is not necessarily guilty of "sedition" since "sedition" requires offensive type language against the US.(He may or may not have used foul language, but unless he did, it's not sedition.)
An argument could be made that because he set out to gain - and release - United States "secrets" he has 'declared war" on the United States.
Traditional warfare includes armed conflict, but given that US law is based on precedent/origins and precise meanings of words, then an understanding of the history of the word is in order.
The English word war derives from the late Old English (c.1050) words wyrre and werre; the Old North French werre; the Frankish werra; and the Proto-Germanic werso. The denotation of war derives from the Old Saxon werran, Old High German werran, and the German verwirren: “to confuse”, “to perplex”, and “to bring into confusion”.
See, if "war" is derived from words meaning confuse, perplex; then certainly it's a reasonable argument that he deliberately set about to "confuse things" for the United States and hence, "declared war," on the nation.
An argument could also be made that release of some of these "secrets" has "aided" our enemies, and that would be true even if the enemies had other ways to gain the same info.