We give a unified treatment of the limit, as the size tends to infinity, of simply generated random trees, including both the well-known result in the standard case of critical Galton–Watson trees and similar but less well-known results in the other cases (i.e., when no equivalent critical Galton–Watson tree exists). There is a well-defined limit in the form of an infinite random tree in all cases; for critical Galton–Watson trees this tree is locally finite but for the other cases the random limit has exactly one node of infinite degree.
The proofs use a well-known connection to a random allocation model that we call balls-in-boxes, and we prove corresponding theorems for this model.
This survey paper contains many known results from many different sources, together with some new results.
"Simply generated trees, conditioned Galton–Watson trees, random allocations and condensation." Probab. Surveys 9 103 - 252, 2012. https://doi.org/10.1214/11-PS188