Menu "Install command line tools" seems to assume write access to /usr/local/bin/stree

This is not necessarily the case.

Ability to link to /Users/jnp/Applications/SourceTree.app/Contents/Resources/git_local/bin/git seems to be enough (to start git at least, havn't tried more).

Xcode is not installed.

From system log:

default 14:53:10.206994+0100 Sourcetree open on /usr/local/bin/stree: Permission denieddefault 14:53:10.206994+0100 Sourcetree open on /usr/local/bin/stree: Permission denied