I am using silent installation parameters (/qb) to provision SourceTree in all our development environments.
It has been working fine till at one point (not so recently) SourceTree was started by default at the end of the installation process.
This makes no sense for unattended/silent installs and also produces a lot of confusion to developers suddenly presented with a SourceTree window when not expected - que increased nummber of confused support calls.
Behaviour is reproducible with 1.10.23.1 and 2.1.2.5. To make it even wierder, calling the setup executable with any parameters will start SourceTree if it has been previously installed.