Symmetric bilinear form/Positivity not on basis/Example/Exercise

Give an example of a finite-dimensional real vector space ${}V$, together with a symmetric bilinear form ${}\left\langle -,-\right\rangle$ on ${}V$, and a basis ${}u_{1},\ldots ,u_{n}$ of ${}V$ such that ${}\left\langle u_{i},u_{i}\right\rangle >0$ for all ${}i=1,\ldots ,n$, but such that ${}\left\langle -,-\right\rangle$ is not positive definite

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