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A parent node $P$ of a node $C$ in a tree is the first node which lies along the path from $C$ to the root of the tree, $R$
Drawn in the canonical root-at-top manner, the parent node of a node $C$ in a tree is simply the node immediately above $C$ which is connected to it.
$$\xymatrix{ & \bullet \ar@{-}[dl] \ar@{-}[dr] & & & \\ \bullet & & {\color{red}\bullet} \ar@{-}[dr]\ar@{-}[dl] & & \\ & \bullet \ar@{-}[dl] & & {\color{blue}\bullet} & \\ \bullet & & & & }$$
Figure: A node (blue) and its parent (red.)
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