A solution is to create an Alias in your .gitconfig and call it easily:
[alias]
tree = log --graph --decorate --pretty=oneline --abbrev-commit
And when you call it next time, you'll use:
git tree
To put it in your ~/.gitconfig without having to edit it, you can do:
git config --global alias.tree "log --graph --decorate --pretty=oneline --abbrev-commit"
(If you don't use the --global it will put it in the .git/config of your current repo.)