Emtree is a list of subject headings unique to Embase*.
Go the Embase home page and click on Emtree
Enter a term in the search box (here - asthma) and add the term to your search as follows.
 Select Explode to include narrower terms in the hierarchy 
Select As Major Focus to narrow results where the term (asthma) is a main topic of articles
 Then either search [Take this query to Disease Search]
Continue with adding more words/phrases [Add to Query Builder]
MeSH (Medical Subject Headings) are used to index articles and other published information in PubMed/Medline. MeSH terms are used in much the same way as Emtree - to include synonyms and find associated broader and narrower terms.
Brief Comparison of MeSH® and Emtree® *
|Terminology is often inverted (e.g. leukemia, myeloid)||Terminology in natural language (e.g. myeloid leukemia)|
|Does not include Emtree terms||Includes all MeSH terms, many as synonyms|
|Many scope notes to define terms or how terms are used or intended; vocabulary more controlled than Emtree||Relies upon author supplied meanings|
|Fewer drug terms (9.250); detailed drug information in supplementary file||More drug terms (31,000+)**; new drug terms added earlier and more often than MeSH; all necessary drug information in Emtree|
|Fewer medical device terms||More medical device terms, including trade name indexing; medical device search form and device subheadings that show relationships to related terms (e.g adverse device events, device comparison, device economics)|
*From A Comparison of Emtree® and MeSH®, a July 2015 Elsevier Whitepaper
**Emtree contains all drug generic names described by FDA and EMA, all International Non-Proprietary Names (INNs) described by WHO from 2000, 23,000+ CAS registry numbers and extended coverage of Trade Names described by many major pharmaceutical companies. From the Elsevier Embase fact sheet, a July 2015 Elsevier Whitepaper
From p. 11 of Embase Indexing Guide 2015
Automatic indexing for selected articles was introduced into Embase in 2009.
Three types of article are indexed in this way:
Automatically indexed articles are indexed with Emtree terms, selected by an algorithm which is applied to the text of titles, abstracts and author keywords.
The algorithm is able to differentiate major and minor index terms; however, candidate terms and subheadings are not indexed. Non-Emtree indexing such as trade names, manufacturer names, clinical trial numbers and molecular sequence numbers is also not indexed.