Why is the plot like that?

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I have tried to plot the following function's level curves by hand and then checked my drawing with wolfram alphas level curve applet and I don't understand why it only plots the left half? In my drawing it is a parabola?

$$z=x+5*\sqrt y$$

EDIT:

Wolfram Alpha Output

My Expectation

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Contrary to what other comment say, the reason is not $\sqrt y$ being undefined for negative $y$. The reason is that $\sqrt y$ is a positive number and you are missing the half-parabola $$z=x-5\sqrt y.$$