if-then-else inside Bash Alias

I would use a function for that, like so:

gitmv()
{
    # If in a git repo - call git mv. otherwise- call mv
    if [ x`git rev-parse --show-toplevel 2> /dev/null` = x ]; 
    then
        mv "$@"  
    else 
        git mv "$@" 
    fi
}

Edit:

alias mv=gitmv