By default, Sourcetree 3.4.9 displays a "Commit" column which contains the short-form changeset ID, like "7f8583abaa83". Mercurial also assigns changesets a number (integer) such as "3059". This is displayed in commit details, but there appears to be no way to display these numbers in the table, even though Sourcetree for Macintosh reportedly allows that following SRCTREE-1572.

TortoiseHg displays a column for that number. I recommend to allow displaying both properties simultaneously, like TortoiseHg, rather than Sourcetree for Macintosh.