Add PowerShell alias to your profile.
function Get-Git { & git $args }
New-Alias g Get-Git -Force -Option AllScope
This will alias g to git, however you forgo the tab expansion.
posh-git shell is replacing default TabExpansion function with own implementation.
To enable tab expansion for the g alias, we need to edit this implemention.
code (Get-Command TabExpansion).ScriptBlock.File
Scroll to the bottom and add the following
function TabExpansion($line, $lastWord) {
$line = $line -replace '^g ', 'git '
...
}
Reference