Is this a BST pre-order traversal?
JavaScript (Node.js), 49 bytes



a=&gt;!a.some((p,i)=&gt;a.some((q,j)=&gt;q&gt;p&amp;a[j+=j&gt;i]&lt;p))


Try it online!

Using the fact that for array \$a_0 ... a_{n-1}\$, \$a\$ is the pre-order traversal of some BST iff \$ \forall 0\le i&lt;j&lt;n; a_i&lt;a_{j-1} \implies a_i&lt;a_j \$ holds.

Thanks to Arnauld, save 1 byte.