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Humans bleed metal too; there's iron in haemoglobin.

It's a different scale. Human blood is well under 0.08% iron, this tree has 25% nickel. So over 300x as concentrated.

PS: 4 grams of iron in a persons body, ~5kg of blood.

The hemoglobin molecule itself only has something like one iron atom per 1000 non-iron atoms.

Yea it's: C2952 H4664 O832 N812 S8 Fe4 so 2315:1.

The fluids also contain various electrolytes, i.e. metal cations. But still nowhere close to those trees.