how are split decisions for observations(not features) made in decision trees
Do i also need to try all the combinations of a feature split, for above case, height &lt; 100 &amp; height &gt; 100, then height &lt; &amp; height &gt; 110 &amp; height &lt; 90 &amp; height &gt; 90 and so on

Suppose that you only have 3 posible values on height 80,90,100. Then the decision tree will try to split on if X &gt;= 80,X &gt;= 90 and X &gt;= 100. If the instance does not satisfy the condition will fall on the other leaf.
So if the split is above the threshold it will fall into another leave, if its below it will fall into another. And then there recursively.

So the answer to this is NO. It will only try on of the logical conditions -- &gt;= for example. I believe this depends on the implementation.
I encourage you to build a decision tree from scratch to fully understand the algorithm.
I reccomend you this video https://www.youtube.com/watch?v=y6DmpG_PtN0 but there is a lot of tutorials there. Choose the one that suits you most.