[LaTeX] Sum equation in LaTeX

\begin{align}
 Bias = \frac{1}{n} \textstyle \sum_{i=1}^{n} \varepsilon_{i} 
\end{align}

\begin{align}
 Bias = \frac{1}{n} \displaystyle \sum_{i=1}^{n} \varepsilon_{i} 
\end{align}