In the documentation for Apache ignite, it states that they provide indexing functionality for RDDS.
Also in the below link we can find methods to create indices.
Is there any documentation on what kind of indices it supports underneath (B-trees, R-trees)
Ignite indexes are either based on
SnapTreeMap  or on
ConcurrentSkipListMap. The former is used for indexes stored in off-heap memory, while the latter is for on-heap.