Pseudo tree builder code

pseudo_code

(A) Initialize a bit mask indicating which samples are contained in each node
(B) Initialize a “node map” indicating which nodes are present at each level
(C) ForEach(tree_level)
    1. Find the node id of all data samples, using the bit mask
    2. Compute the possible splits for all bins, all columns and all nodes
    3. Find the best split for each node
    4. Update the bit mask and sparse node map to feed the next level