Here's part of my ~/.gitconfig.global
[user]
name = Jared Forsyth
...
[alias]
# View the tree!
tree = log --oneline --decorate --all --graph
tr = log --oneline --decorate --all --graph
t = log --color --date-order --graph --oneline --decorate --simplify-by-decoration --branches
ta = log --color --date-order --graph --oneline --decorate --simplify-by-decoration --all
# other aliases that are so useful
st = status
s = status
c = commit -v
p = pull
b = branch
co = checkout
su = submodule update --init --recursive
mt = mergetool
ld = log --decorate
g t is the short form: it only shows branches & tags (no intermediate commits)

g tree (or g tr) is the long form -- it shows all the commits, with branches annotated

g a is just like g t, but it also includes remote branches and stashes.