The node of a binary tree is called a single child if it has a parent but does not have a sibling. The root is by definition not considered a single child.
Let $T$ be a binary tree of size $n$, and let $k$ be the number of vertices in $T$ that are single children. Is it true that if $\frac{k}{n}\leq \frac{1}{2}$ then the height of $T$ is $O(\log n)$?